Para-bromoacetanilide has a plane of symmetry

1,2-dimethyl-3,4-diisopropyl-cyclobutadiene-iron tricarbonyl and trimethyl-isopropyl-cyclobutadiene-iron tricarbonyl

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1 75.2-dimethyl-, 4-diisopropyl-cyclobutane-iron tricarbony trimethyl-isopropyl-cyclobutane-iron tricarbonyl 1,2-dimethyl-, 4-diisopropyl-cyclobutane-irontricarbonyl and trimethyl-isopropyl-cyclobutane-irontricarbonyl HANS ALBERT PETER BRUNE, HANS and HANS HÜTHER * Department of Organic Chemistry, University of Ulm ** (Z. Naturforsch. 2 b, [97]; started on May 5, 97) Thermal cyclization of 2,9-dimethyl-deca-, 7-diyne yields, 4- bismethylene-1,2-diisopropyl-cyclobut-1-ene. This forms by addition of two molecules of hydrogen chloride at 78 several with respect to the positions of the four alkyl substituents isomeric fra / is-, 4-dichloro-dimethyl-diisopropyl-cyclobut-l-enes. The reaction of this mixture of isomers with diiron-enneacarbonyl, 2-dimethyl-, 4-diisopropyl-cyclobutane-irontricarbonyl is obtained a 2% yield. Trimethyl-isopropyl-cyclobutane-irontricarbonyl has been prepared by an analogous route from 8-methyl-nona2, -diyne. Chemical properties and spectroscopic data of these complexes are discussed with respect to structure and bondg. In the course of investigations, the effects of tuent on metal complexes of cyclobutane via substituents. 2 - D i m e t h y l d i i s o p r o p y l - c y c l o b u t a d i e n - iron tricarbonyl trimethyl cyclobutane iron - observed t r i c a r b o n y l f o r t. About the representation of the property that the persistence of the system cyclobutates and ser v e r combinatio ns should be reported here. N-iron tricarbonyl decreases considerably with increasing number of A l k y l substituents on V i e r r i n g-4. Syntheses In the alkylated nickel complexes cyclobutane, on the other hand, ratios are exactly the opposite - .2-dimethyl-diisopropyl-cyclobutane: here only tetra-alkylating iron tricarbonyl th complexes are sufficiently stable Influences of hexa- .5-di () were first to analyze liquid substituents for properties of cyclobuta- ammonia at 5 with diisopropyl sulfate diene-metal complexes, syn- chronously of n atrium amide to 7-methyl-octadiyne we discussed among other things ee range of cyclobutane (2) alkylated. I m A u t o k l a v e n, with D i i s o p r o - e i s e n t r i c a r b o n y l e n u n d varied d a b e i s o w o h l pyl sulfate number as well as the large alkyl substituents D i m e t h y l - i n 2 ~ 4 i. This turned out to be the properties of connections only dependent on the number of alkyl substituents, their character- e thermal second cyclization () based on the representation of the formation. at 495 which resulted in bismethylene cyclo- bu t e n 7 from H e x a d i i n. 4 - B i s m e t h y l e n d i - ter i n s b e s o n d e r e d e m substituent volume isopropyl cyclobut-l-en, however, independently. To complete 78 our isopropyl radical absolute (4). Aether These two molecules stored in chlorine- V o r s t e l u n g e n u e r e r e r e e r e ction, we put hydrogen under the image, and inevitably position- Investigation with synthesis and d e m e lution A l k y l g r u p p e n i s o m e r e study of special pressure requirements to Prof. Dr. Dr.-Ing. Prof. Prof. Prof. Prof. Prof. Prof. Prof. Prof. to Prof. Dr. rer. nat. A. BRUNE, Univ. Ulm, Center for Chemistry-Physics-Mathematics, D-7500 Karlsruhe, Richard-Willstätter-Weg. * New address: Glanzstoff A.G., Obernburg / Ma. ** Current address: Institute for Organic Chemistry, University of Karlsruhe / Germany. H. A. BRUNE, W. EBERIUS, and H. P. WOLFF, J. organometall. Chem. 2,485 [98]. 2 H. A. BRUNE, H. P. WOLFF and H. HÜTHER, Tetrahedron [London] 24, 48 [98] Jrans-.4-dichloro-A. BRUNE and H. P. WOLFF, Tetrahedron [London] 25, 089 [99]. H. A. BRUNE, H. P. WOLFF and H. HÜTHER, Tetrahedron [London] 27 [97], in press. H. A. BRUNE, H. P. WOLFF, W. SCHWAB and H. HÜTHER. Tetrahedron [London] 27 [97], in press. R. A. RAPHAEL and F. SONDHEIMER, J. chem. Soc, 2 0. W.D. HUNTSMAN, and H.J. WRISTERS, J. Amer. chem. Soc. 85, 08 [9]. This work was published in the year 20 by the publishing house Zeitschrift für Naturforschung, in collaboration with the Max Planck Society for the Science of Science. digitized published under follow license: Creative Commons Attribution 4.0 license. This work has been digitalized and published 20 by Verlag Zeitschrift für Naturforschung cooperation with the Max Planck Society for the Advancement of Science un a Creative Commons Attribution 4.0 International License.

2 A. BRUNE, P. WOLFF AND HÜTHER 7 dimethyl-diisopropyl-cyclobut-l-ene (5 a 5 d). The isolation of individual isolates did not succeed, T (CH,) 2cH0], s02j ven CH-C H-CHC-CH2 ^ VCCH Y + CH obviously more _HCL_ CH 2 ET (CH) 2CH - ^^ CH2 4 (CH) 2 CH V + CH enen + (CH) 2CH ^ TC CH (CH) 2CH ^ H) 2+ CH'V- CH (CH) 2 + CH ^ position From the alkyl groups () 2 8% yield as light yellow oil receive. 7 [(CH); CHQ]; SO; k CH-CC ~ CH2 CL- ^ CH CC CH2 CH 8 YfCH2 (CH) 2CH '^ jCH2 over (CH) 2CH-! also '- "S solid- CH (CH) 2 (CH) 2CKT ^ CH, because the proprons required for this are missing directly on the four-ring bonded. Structure, bonding ratios From the isomer mixture 5 a 5 d, with pentane () trimethyl- Liquid isopropyl-cyclobutane-iron tricarbonyl iodide [98] .. 2-dimethyl-.4-diisopropyl tuentene of the precursors of (immediately adjacent isopropyl groups 4) following- * 5 b 5 d sd spectroscopically indistinguishable as mirror-image isomers. ** The circle in the quadrant is not intended to indicate a symbol of aromatic character, but merely to indicate experimentally proven indistinguishability of bonds. 8 R. CRIEGEE, W. EBERIUS AND OTHERS BRUNE, Chem. Ber. 0, 95 the order results from the arrangement of the substituents initially with ammonia in the arrangement of the substituents n d u n g 2% e u p e u t e F o r m b l a ß g e l b e r crystals. () Properties. 2-Dimethyl-.4-diisopropyl-cyclobutane-iron tricarbonyl Hexa-.5-di CH ^ Ojh Fe (CO) resonance spectra was not possible in this case - Diisenenneacarbonyl CH 0a '* CH Fe2 (CO) 9 analysis carried out P rotons - CH CH 0 b '* 0 formation of steric arrangement as for example by 9 CH in this example Jrans position chloro - atoms immediate I 0 a the steric process a dition of chloro what is Cl ru _2H L CH bismethylene cyclobutene8 (m.p. rearranged. On the basis of previous investigations. C. 8 '0 b C CHJ ean Ee 0 a,) the isomer mixture is set. expect. iso frans-position e mixture of isomers Therefore, for the subsequent complex formation to chlorine, trimethyl - isopropyl - cyclobutadiene - iron tricarbonychroma tographs (0 0; Sil.) or, in the case of column zueancycli (9), CHS zen tillativ could not be separated and in the gas - to become, (0 a, 0 b), en C hlor - atoms probable because they are due to low boiling point differential autoclave with diisenenneacarbonyl P entanbei H) 2 apparently obtained in (CH) 2CHY + CHCH) 2 W-Fe (CO) (CH) 2CK ^^ CH ** chromatography 0.4-dichloro-trimethyl-isopropyl-cyclobut-1 take. 5b FE2 (CO) 9 (8) borrowed (vg l. 5 a 5 dun dc 8 '9) 5a + 8-methyl-nona-2.-di (7) from this hydrogen arose from this e mixture of two CH-C ( CH could sate. By addition of two molecules CH - CH - CC - CH 2 CH to the heptadiyne diisopropyl sulfate len-l-methyl-2-isopropyl-cyclobut-l-ene 2 CH t (ch}); ch0] ; s02> with that in the nitrogen flow at m. 4 - bismethylated; liquid ammonia / n atrium amide CH was from n atrium amide 9 H. HÜTHER UH im Drude. A. BRUNE, Organ. Magnet. Res. [ 97], R. ed. Seances Acad. Sci. 85, 28 D. HUNTSMAN UHJ WRISTERS, J. Amer. Chem. Soc. 89, 4 2 [9 7]. * 0 a 0 a 'or 0 b 0 b 'as each spectroscopically indistinguishable mirror image isomers.0 M. URION, [927]; WC

3 low complex formation was carried out under very mild pen 77 sbesone to r e a c ti o n s c e d i n g u n g u n g s (v g l. Experimental mood part); Ee migration of alkyl groups on the four-C () ring can therefore be viewed as very unlikely carbon atoms C (l) CH Gr couplings (ie C () uniform cross-CH hybridizations C () therefore cannot be ruled out with certainty A definition of a definite substituent arrangement, independent of the synthesis, follows from the proton resonance spectrum: For the unsubstituted II cyclobutane-iron tricarbonyl proton resonance spectroscopic investigations of nematic-crystalline liquids, analyzes 2C H proton resonance spectrum C H coupling constants indirect in and ultimately un- Distance determinations n diffraction 2 gas state4 by means of ee Electro-quadratic structure four rings with uniform C C bond orders. Proton resonance spectroscopic investigations on mono - also overes proved accordingly Timmed atoms) ee through valence root C (2) at C (4) sen hthrough- h e n d e perpendicular to th e m e r r i n g lying plane of symmetry. If the dimethyl-diisopropyl-cyclobutane-iron-tricarbonyl arrangement described here had substituents-dimethyl-2,4-diisopropyl, carbon atoms C (l) C () C (4) would or would be replaced by C (2) In each case, a symmetry plane perpendicular to the four-ring plane. Go through the second symmetry plane through () sequence. would be magnetically equivalent to both m e t h y l g r u p p e n within each of the r I s o p r o y l A g r u p p e. The methyl proponons B of both isopropyl groups should therefore be in the proponene-substituted cyclobutadiene iron tricarbonylene X - CO - CH 5, CH5 -, CH - 7, Cl - (A: 7'8) resonance spectrum through K coupling with the respective tertiary existence of carbon atoms C (l) causes C () passing through for the trimethyl- In fact, however, a double doublet with two cyclobutane-iron tricarbonyl (B; RH) different vicinal coupling constants becomes the 2 'trimethyl- ethyl cyclobutane iron tricarbonyl, 5 Hz; Proton isopropyl group as a uniform doublet / 2 7.0 Hz).appeared. This (J double existence of a doublet structure due to C (2) is retained even at higher temperatures - C (4) through and both connections; it cannot therefore be typed by ee (A or B) hte rotation of the isopropyl groups (B; R C2H5) quadrants 9 in each case perpendicular to the plane of symmetry. Analogous to this, this work also contains methyl-isopropyl-cyclobutane-iron tricarbonyl non-equivalent. This non-equivalence is, however, within () within each isopropyl group caused by methyl groups magnetically on the basis of magnetic equivalence P roto - present four-ring systems with the structure at C (l) nn and C () bonded methyl coincide H-couplings sen both methyl groups CS YA N N O N I, G. P. CEASAR and B. P. DAILEY, J. chem. Soc. 89.28 [97]. 2 direct H. A. BRUNE, H. P. WOLFF and H. HÜTHER, 485 [98]. Amer. Chem. Ber. 0, V i e r r i n g result, substituents H. A. BRUNE, H. P. WOLFF and H. HÜTHER, 4 2 b, 84 [98]. OBERHAMMER et al. 07 [99]. 5 H. A. BRUNE, H. H Ü T H E R, BRUNE, 7 R. Magnet. Res., 52 [99]. Z. Naturforsch. Z. Naturforsch. 24 a, W O L F U. I. KÖRBER, Organ. Sequence. 2 - D i m e t h y l d i i s o p r o p y l carries 8 assumed- 9 A. BRUNE, H. HANEBECK and H. HÜTHER, Tetrahedron [London] 2,099 [970]. H. HANEBECK, dissertation, Univ. Ulm 97. A. BRUNE, HÜTHER, G. HORLBECK and H. HANEBECK, organ. Magnet. Res. [97], in press; A. BRUNE U. G. HORLBECK, Z. Naturforsch. 25 b, 2 [970]. H. A. BRUNE, H. P. WOLFF and H. HÜTHER, Tetrahedron [London] 27 [97], in press.

4 A. BRUNE, P. WOLFF AND HÜTHER 78 so that it contains four asymmetrical carbon atoms, constant 7, 2, Hz measured. These of which C (l) became C (2) and C () C (4 ) In the trimethyl-isopropyl-cyclobutane-eisentricarerscheen () two isopropyl residues in connection with values ​​7.0, 5 H z convincingly confirmed. each have opposite con n f i g u r a t i o n. bonyl here methyl groups proton resonance spectrum The has different coupling constants as well as non-equivalences den m e t h y l g r u p p e n proto-isopropyl residues as fol o l g e co p l u n g with the p r o t o n a m ter- their cause obviously e prop b i n d u n g iso- tiary as iso- tiary they sd magnetically equivalent. shows ee by C (2) These C (4) equivalence hthrough atoms at each plane of symmetry C () C (4) which is perpendicular to plane V i e r r i n g s. Their existence is confirmed by the search part given in C ()) both methyl groups at C (l) (see above *. On the basis of this symmetry sd also bonds C (2) C (l) C (2) C () in each case or C (4) C () pairwise equivalent. Sem bonds symmetry- C (1) C (2) halved). This statement is secured by comparing the total a s y m e t ric. 2-dimethyi - isopropyl-cyclobutane-iron-tricarbonyl on the other hand. The isopropyl radical, viewed from the respective tertiary carbon atom, is asymmetric, therefore electronically and C (4) with carbon on the plane of four rings, plane, magnetic equivalence is asymmetric (the V still contains ee perpendicular magnetic can If there is a temporally stationary struc- tural reference to the isopropyl group anisotropic mole- ture, the residue (gun butane-iron tricarbonyl) produces isopropyl - a cyclically conjugated diene with renating double and single bonds to (or 2-dimethyl) --isopropyl-cyclosten eer higher-symmetrical electron distribution group, despite their quasi-free rotatability, ruled out that C (2) or C (4) fourrgs become indistinguishable from the two outgoing bonds, so that the residual molecule of the proton resonance spectrum! ) the former are divorced. Investigations or structure approximately proven quadratic quadratic (rhombic) properties given to the iron plex plex: cyclobutane 2-8 kom- confirmed. consistently. In the case of T e m p e r a t u r e n o b e r h a l b 9 0 w i r d decomposition (pay attention to the development of CO. Resistance to resinification) to observed oxygen, similar to anene tetra-alkylated, cyclo-butane-iron tricarbonylene> 4 is reduced to unsubstituted cyclo-butane-tricarbonyl. Am for iso-.2-dimethyl-isopropyl-cyclo-butane-iron tricarbonyl group coupling constants The occurrence of vicalen vicale two strongly differing coupling constants is evidently ee t y p s; The phenomenon could also be observed in the ethyl-substituted cyclobutane-iron tricarbonyls 2 '4. In contrast, due to the isopropyl group on a symmetry plane, there are carbon atoms of both methyl groups isopropyl radicals magnetically equivalent; they therefore coop e l n with the tertiary proton. The coupling constant proton-proton coupling constants propyl group: vicalen characteristic peculiarity investigated molecules - and sd with exclusion of oxygen at low temperature (refrigerator) ee such considerable polarization electron distribution that it becomes independent Averaging over two observed vicale coupling constants. Isopropyl coupling constants between the tertiary proton and the protons in the case of magnetically non-equivalent methyl groups were an experimental part ! two surprisingly very different coupling synthesis. 2-Dimethyl-.4-diisopropyl-cyclobutane-iron tricarbonyl () * For a detailed demonstration of the derivation of the plane of symmetry from magnetic equivalence see c. 5'7-methyloc ta-l, 5-di (2): To a freshly prepared suspension, moles of sodium amide, 2 l of liquid ammonia was added at 5 (C02 / methanol)

5 with vigorous stirring a solution 8.2 g (. 0 mol) hexa-.5-di () 40 ml absolute ether within 0 M. added dropwise to complete salt formation for a further hour. Stirred. 7 g (0.5 mol) of diisopropyl sulfate 40 ml of ether were then added dropwise, likewise at 5 within hours of solution, and the reaction mixture was then stirred vigorously for 5 days at this temperature. After the ammonia had been removed, ether was added to the remaining Rütand and then slowly hydrolyzed. The phases were separately etherified four times. Then combined ethereal solutions were washed with 2N sulfuric acid, sodium bicarbonate, sodium chloride solution and dried over magnesium sulfate. Finally, the solvent was distilled off via a packed column (50 cm). The residue was fractionated in vacuo. In addition to 2.4 g of the recovered (conversion 45%, based on), 4 g of already doubly alkylated 2,9-dimethyl-deca-.7-di (), 0.2 g (yield 2%, based on converted) 2 with a boiling point / 2 Get torr. The connection was uniform by gas chromatography (P G; 0). C 9 H 2 (20.2) calc. C 89.9 Found: C H 0.07, H 0.02. H-NMR spectrum (CC 4; TMS after hours): <5, ppm (d; 7.5 H z; rel. Int.): CH isopropyl group;, 90 (complete mult. By coupling with both CH 2 groups; Int.): Acetylene proton; 2, (complete. Mult; Int. 4): CH 2 groups; 2.48 (Sept .; 7.5 Hz; Int.) R C H isopropyl group. (CC 4): r (ch): 285 cm "; r (CC): 220 cm Dimethyl-deca-.7-di (): To a suspension 0.75 mol of sodium amide 400 ml of liquid ammonia (5) were added under vigorous stirring as shown in illustration 2, so first 0.0 g (0.28 mol) 2 50 ml absolute ether then 80.0 g (0.44 mol) diisopropyl sulfate 00 ml ether added After warming to room temperature, the autoclave was shaken overnight. Work-up as in 2. 7.0 g were recovered from the second 2 (conversion 4%). Yield of: .8 g (9%, based on converted 2). S d p. 9 / 5 Torr. The substance was uniform by gas chromatography (PG; 0). C2H8 (2,) Calc. C 88.82 found C 88.50 H, 8, H, 00. ^ - NMR spectrum (CC 4; TMS n. S t d.): Ppm (d, 7, H z; rel. Int.): CH propyl groups; 2.28 (sp. Sg .; CH 2 groups; 2.5 (sept .; 7, H z; CH isopropyl groups. <5 Int. Int., 4 Iso2):): 79 (CC 4): v (CC) not observable, w eil approximated I R ia; otherwise only oscillation bands of isopropyl methylene groups are observed, and weighing can be dispensed with. cyclized according to HUNTSMAN W R I S T E R S 7 TO 4. However, it was not possible to subsequently recover 4 by fractional distillation. Even a gas chromatographic cleaning evidently did not lead to success due to the strong tendency to polymerize. Therefore, 4 was processed further without redrawing to 5 a 5 d (see below). According to the analytical gas chromatogram, the sample used (P G; 0) contained 9% 4 and 24% unreacted two components that were not further identified with 5 and 7 percent respectively. The elemental analysis of the mixture indicated that the component appearing at 5.% also evidently had an isomeric composition of C 2 H 8. C2H8 (2,) Ber. C 88.82 H, 8, found C 88.8 H, 2. H-NMR spectrum (CC 4; T M S n. S t d.); Signals for 4 were determined from the isomer mixture: <5.22 ppm (d; 7 7.0 H z; rel. In.): CH isopropyl groups; 2.77 (Sept .; 7 7.0 H z; Int.): C H isopropyl groups; 4.52 4.59 (sp. Sg .; Int. +): Methyl protons; Average coupling constant cannot be determined. (Noun): r (CC) 98 cm ", r (C CH 2) 49 cm", y (CH 2) 849 cm - ". Trans-.4-dichloro-dimethyl-diisopropyl-cyclobut-1 -ene ( 5 a 5 d): In a solution, 4 g (0.029 mol) 9 percent A moderate stream of hydrogen chloride was passed in until the volume of the solution had reached 0 ml. The reaction mixture was stirred for 24 hours at 7 8, warmed to room temperature within a day, finally excess hydrogen chloride was stripped off with the ether. Fractional distillation gave residue, 85 g (00%) ees mixture of isomers 5 a 5 d with a boiling range / 0, 0 Torr.Ee tillative or chromatographic separation of isomers did not succeed because they evidently rearranged or partially split off hydrogen chloride under the separation conditions (e.g. Sil .; 0 0 o in column chromatography). C oh 2 0 Cl 2 (25.2) calc. C, 28 Gef. C, 5 H 8.57 H 8.29 Cl 0.5, Cl 28, dimethyl-4-diisopropyl-cyclobutane-iron tricarbonyl (): To a vigorously stirred suspension 2.4 g (0.04 M ol) Diisenenneacarbonyl ml dry pentane was excluded

6,770 atmospheric oxygen (N 2) ee solution 4.0 g (0.07 mol) of isomer mixture 5 a 5 d is added dropwise, the reaction mixture is first heated under reflux (bath temperature 40) for two hours. Then the insoluble matter was filtered off from the filtrate, the solvent F e (C O) 5 formed during the reaction was stripped off. The residue was extracted with pentane and the eluate was fractionated on aluminum oxide (Woelm neutral, activity level). In the fraction passing over at 8 9/0.0 2 Torr, 08 g (2%) were recovered. To complete the purification, pentane was chromatographed again, fractionated and finally recrystallized from pentane at 78. Pale yellow crystals with a melting point of 4. Molar weight (mass spectrometry): 0 4 for the main isotope 5 Fe. C 5 H 2 O FeO (04.2) calc. C 59.2 H, Fe 8 ,, found. C 59.20 H, 55 Fe 8.29. H-NMR spectrum (CC 4; TMS n. S t d.): <5.0 ppm (d; 7.5 H z; rel. Int.), 7 (d; 7 7.0 H z; Int .): magnet, non-equivalent CH groups within each isopropyl radical;, 82 (s; Int.): methyl protons; 2.29 (complete Mult .; Int.): C H isopropyl groups. (CC4): V (C 0) A I 204 cm ", R (C 0) E synthesis 958 cm". Trimethyl-isopropyl-cyclobutaneisentriearbonyl () 8-methyl-nona-2.-di (8): 2.0 g (0.25 mol) hepta-.5-di (7) 0 40 ml absolute ether, 80.0 g (0.44 mol) diisopropyl sulfate 75 ml of ether 0.75 mol of sodium amide 400 ml of liquid ammonia were shaken overnight in the autoclave as shown, the reaction mixture was worked up accordingly. From the converted 7, 8 g were recovered (conversion 40%). 4 g of 8 (yield 48%, based on converted 7) with a boiling point of 5/1 0 Torr were obtained. The substance was uniform by gas chromatography (P G; 0). C 0 H 4 (4.2) calc. C 89.49 H 0.5, found C 89.4 H 0.5. H-NMR spectrum (CC 4; TMS n. S t d.): <5.2 ppm (d, 7.5 H z; rel. Int.): CH isopropyl group;, 75 (Mult .; Int.) : Methyl group; 2.2 (Mult .; Int. 4): methylene groups; 2.50 (sept .; 7.5 H z; Int.): C-H isopropyl group. (CC 4): no characteristic bands (cf.) .. 4 - bismethylene -methyl- 2- isopropyl-cyelobut- -en (9): 5.0 g (0. mol) 8 were in a nitrogen flow 0 / hour . cyclized. Distillation gave 9.8 g of 9 (yield 5%) from Spd. 5 2/0 Torr obtained. The connection was gaschromato20 R. B. KING,: Organometallic Syntheses, Edited by J. J. EISCH and R. B. K I N G, Vol., P. 9, Academic Press, New York 95. graphisch (P G; 40) uniform. C0H4 (4.2) calc. C 89.49 H 0.5, found C 89.7 H 0.24. H-NMR spectrum (CC 4; TMS n. S t d.): <5.9 ppm (d; 7 7.0 H z; rel. Int.): CH isopropyl group;, 7 (s; Int.) : Methyl group; 2.7 (sept .; 7 7.0 H z; Int.): C 1 -C H isopropyl group; 4, (s; Int.), 4.8 (s; Int.) 4.4 (s; Int. 2): methylene protons; common coupling constants not recognizable. (CC 4): v (C C) 700 c m ", r (C CH 2) 40 c m", y (C H 2) 852 c m -. trans -.4-dichloro-trimethyl-isopropyl-cyclobut-enes (0 a - 0 b): In ee solution, 5 g (0.08 mol) 9 40 ml of absolute ether was passed at 7 8 hydrogen chloride until the Volume had reached about 70 ml. Then it was continued as in 5. 0 g (90%) of isomer mixture 0 a, 0 b with a boiling range of 8/4 Torr was obtained. A separation of isomers did not succeed, as in the case of 5, as a result of mutual conversion. C 0 H C 2 (207.2) calc. C 57.98 H 7.79 Cl 4.2, found C 58.2 H 7.72 Cl, 5. Trimethyl - isopropyl cyclobutane - iron tricarbonyl (): To a vigorously stirred suspension 0.9 g (0.0 mol) of diironeneacarbonyl ml of dry pentane, 0 g (0.05 mol) of isomer mixture 0 was added under a residual nitrogen atmosphere a, 0 b 20 ml of pentane are added dropwise and the reaction mixture is heated under reflux at a bath temperature of 40 for two hours. Then the insoluble matter was filtered off from the filtrate, the solvent Fe (CO) 5 formed during the reaction was stripped off. The residue was extracted with pentane and chromatographed on aluminum oxide (W o e l m neutral, activity level). The distillation of the eluate at boiling temperature gave 4 9.5 / 0.02 Torr., 4 g (yield 28%) as a pale yellow oil. M.p. mol. Wt. (mass spectrometry): 27 for the main isotope 5 Fe. C H F e 0 (27,) Ber. C 5.55 H 5.84 Fe 20.2, found C 5.80 H, 05 Fe 20.5. H-NMR spectrum (CC 4; TMS n. S td e.): <5.2 ppm (d; 7.7 Hz; rel. Int.): CH isopropyl group;, 77 (s; Int.), 78 (s; Int.): methyl groups; Sgulett structure signals their half-widths (0. Hz) do not change when switching to benzene or dichlorobenzene as solvent; 2.42 (sept .; 7, 7 H z; Int.): C H isopropyl group. (CC 4): v (C 0) A i 207 c m ", v (C 0) E 957 c m". We would like to thank the German Research Association of the Chemical Industry Association for generous support of this study.