Cyclopropanes from cyclic ketones

This procedure illustrates a new three-step reaction sequence for the one-carbon ring expansion of cyclic ketones to the homologous tt,/3-unsaturated ketones. The key step in the sequence is the iron(III) chloride-induced cleavage of the central bond of trimethyl-silyloxycyclopropanes which me obtained by cyclopropanation of trimethylsilyl enol ethers. The procedure for the preparation of 1-trimethylsilyloxycyclohexene from cyclohexanone described in Part A is that of House, Czuba, Gall, and Olmstead. ... 

The electronic state responsible for reactions II and III is not so well known and it is almost certain that there are essential differences in this respect between the different cyclic ketones. On the basis of the different pressure dependence of propene and cyclopropane formation in the direct photolysis of cyclobutanone, McGee concluded that cyclopropane is formed from the excited singlet state, while propene is considered to be a triplet product. 

Unsaturated cyclic ketones also underwent the Kulinko-vich reaction (Scheme 1.199) [280]. Cha and coworkers reported that methoxycyclohexene 421 underwent to form spiro cyclopropane 422 in good yield by treatment with Grignard reagent and Ti(0-/-Pr)4. Tricyclic cyclopropanes 424 were successfully prepared from vinylic cyclohexene derivatives 423. 

Cyclic p-kcio esters and )9-diketones (596) smoothly effect ring-opening of 1,1-bis(benzenesulphonyl)cyclopropane (412) under basic conditions. Reductive cleavage of the resulting sulphones (597) by lithium arylides provides routes to 598 and 599 (equation 210) The bis-benzenesulphonyl compound appears to fulfil the requirements for a propylene 1,3-dipole. The fact that the sulphones can be sequentially removed permits selective introduction of from one to three electrophiles (E) (equation 211). In the case of )5-keto esters, such versatility created a novel three carbon insertion between the ester group and the ketone or a cyclopentane annulation. ... 

The use of the carbanion derived from the chloroallylphosphonate (163) in the enantioselective synthesis of cyclopropanes (164) by Michael addition to a,P-unsaturated ketones has been the subject of a short review (Scheme 18). Denmark s group have published full details of the asymmetric Michael addition reactions of cyclic enones with carbanions derived from l,3,2-oxa2aphosphor-inane 2-oxides (165) and (167). y-Addition to give (166) predominates although the extent of this depends on the ring size of the Michael acceptor. The level of diastereoselectivity depends on the stereochemistry of the allylphosphonate used ... 

Johnson et al have used the availability of the above reaction to study further the overall mechanism of the reaction of sulphonium and oxysul-phonium ylides with carbonyl compounds and a 3-unsaturated carbonyl compounds. The contrasts between these two types of ylides are well known and can be exemplified as follows (i) in reactions with cyclic carbonyl compounds, sulphonium ylides attack from the axial position while sulphoxonium ylides attack from the equatorial position (ii) in reactions with a/3-unsaturated ketones, sulphonium ylides react at the carbonyl group to form oxirans while sulphoxonium ylides react at the olefinic group to form cyclopropanes. These results can be explained by considering the reversibility of the initial step of each ylide reaction and whether the reaction is subject to kinetic or thermodynamic control. 

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