ROBERTA. BENKESER AND EVERETT W. BENNETT
5414
[CONTRIBUTION FROM
THE
Vol. 80
CHEMICAL LABORATORIES OF PURDUE UNIVERSITY]
A Silicon Analog of Cyclohexanone. The Preparation and Reactivity of 4,4-Dimethyl-4-silacyclohexanone BY ROBERTA. BENKESER AND EVERETT IV. B E s m T ? RECEIVED APRIL 5, 1958 A silicon analog of cyclohexanone, 4,4-dimethyl-4-silacyclohexanone, has been prepared in a four-step synthesis and i t s reactivity compared with its carbon analog, 4,4-dimethylcyclohexanone. The dissociation constants of the cyanohydrins of these two ketones have been determined, and the results interpreted in terms of the I-strain theory. Spectral evidence is presented which would indicate that the ring size of the silicon ketone is somewhat larger than that of its carbon analog.
The literature contains a rather considerable number of examples of cyclic organosilanes. However, probably as a result of the synthetic difficulties involved, there has been only one example of a cyclic silane reported which contains a functional group in the ring itself.2 It seemed particularly desirable to investigate the chemistry of such compounds to ascertain whether the presence of the bulky silicon atom would in any manner alter the reactivity of the functional group. Toward this end we are hereby reporting the successful preparation of 4,4-dimethyl-4-silacyclohexanone (I). The dissociation of the cyanohydrin 0
I!
/\ >si( I CH3
CH3 I
of this compound has been measured as well as that of its carbon analog, 4,4-dimethylcyclohexanone. Syntheses.-The synthesis of 4,4-dimethyl-4silacyclohexanone was accomplished by the reaction sequence pyridine + 2HO(CH2)rC1---+ ( C H ~ ) ~ S ~ [ O ( C H Z )(85%) IC~IZ ( C H ~ ) Z S ~ [ O ( C H Zf) ~SCa~+ ] ~ (CH&SiCl -+ (CH&SiC12
Hz0
--+ (CH~)ZS~[(CH&OHIZ (57%
(1)
(2)
An attempt to prepare the dibasic acid (equation 3) uia the sodium salt of malonic ester failed because of a surprisingly facile cyclization which occurred resulting in the formation of a silacyclobutane. Despite the presence of a 200% excess (CH&Si(CH&1)2
+ 2NaQ CH(C02Et)2B
4
[ (CE13)2SiCH2C(C0~Et)~CH3] 2 0 19% (11)
of diethyl malonate, a 7 5 ~ 7yield ~ of 1,l-dimethyl3,3-dicarbethoxysilacyclobutane was obtained. Previously4J these conditions had been employed successfully to avoid cyclizations in similar reactions. The physical properties of the silacyclobutane agreed well with those previously reported for this compound by West.8 The disiloxane structure (compound I1 above) was not rigorously established. An elemental analysis agreed well for the compound shown and an infrared spectrum showed the presence of a siloxane linkage. The formation of such a material could be rationalized easily in terms of a base-catalyzed ring opening of 1,l-dimethyl-3,3-dicarbethoxysilacyclobutane.The ethOEtg ( C H ~ ~ ZCII, S ~ < ~ ~ ' ) C ( C O---+ O EtOH E~)~ CH3
I 1
EtOSiCHX (COOEt)&H3 CHI
350"
Thorium salt
+ 25 mm.
I (35-40%)
(5)
The thorium salt was used for the final ring closure (step 5 ) in view of the study by Ruzicka, et u L . , ~ on the pyrolytic closure of various sized rings by the use of heavy metal salts. (1) (a) A. Bygden, BEY.,48, 1236 (1915); (b) R. H. Krieble and C . A. Burkhard, THISJOURNAL, 69, 2689 (1947); (c) R. West, i b i d . , 76, GO12 (1954); (d) 77, 2339 (1955); (e) L. H. Sommer and coworkers, ibid., 79, 1008, 3295 (1957). (2) A silacyclopentene has been reported; see A . D. Petrov and co-workers, Bull. A c a d . Sci. U.S.S.R., Diu. Chem. Sci., 6 , 861 (1955). Unfortunately we have not yet been successful in duplicating the results of these worker.;. (3) L. Ruzickn, 'A'. Brugger, M. Pfeiffer, H. Schinz end 11 Stoll, El&. Chiill. :i;Ld, 9, 339. 499 (1926).
oxysilane thus produced would quite likely condense to the disiloxane during the process of isolation. Saponification of compound I1 produced a tetrabasic acid which could be decarboxylated to a product which analyzed reasonably well for some type of cyclic anhydride. Since these reactions were not directly connected with the main phase of the project they were not investigated further. Consequently it must be emphasized that structure I1 must be considered as only tentative. Compound I was reduced successfully with lithium aluminum hydride in GGYo yield to 4,4dimethyl-4-silacyclohexanol. The synthesis of 4,4-dimethylcyclohexanonewas accomplished by the sequence (4) J. Cason and C . F.Allen, J . Ovg. Chem., 1 4 , 1063 (1949). ( 5 ) A T. Blomquist and J . TTolinsky, i b i d . , 21, 1371 (19SA). (b) I
