Stereoselective acid-catalyzed homoallylic rearrangement of cyclopropylsilylmethanols: an efficient route to Z-homoallyl derivatives

Treatment of cyclopropylsilylmethanols derived from cyclopropyl silyl ketones with acid catalyst gives the corresponding silyl-substituted homoallyl derivatives in high yields with good stereoselectivity, independent of the substituents on the cyclopropyl ring. Cyclopropylsilylmethanols having a n-, s-butyl or phenyl group on the carbinyl carbon react to afford the E-homoallyl derivatives selectively. On the other hand, the reaction of cyclopropylsilylmethanols having a tert-butyl group gives Z-isomers exclusively. The following protiodesilylation of the resulting homoallyl derivatives proceeds with retention of configuration.     

Synthesis and rearrangement reactions of 1,4-dihydrospiro[1,4-methanonaphthalene-9,1′-cyclopropane] derivatives

Reactions of benzyne with ester derivatives of spiro[2.4]hepta-4,6-dien-1-ylmethanol were performed. By rearrangement reaction of cyclopropyl methanol units of ((1s*,1′R*,2R*,4′S*)-1′,4′-dihydrospiro[cyclopropane-1,9'-[1,4]methanonaphthalen]-2-yl) methyl 3,5-dinitrobenzoate (13) and its isomer (14), corresponding allyl chlorides were obtained. Two rearrangement products were obtained from bromination of compound 13 with an equivalent amount of Br₂. A naphthalene derivative including allyl and CHO moiety was formed for reactions from compounds with epoxide of 13 and 14 with NaN₃ by sequential rearrangements. Formations of products are discussed.     

Acid-catalyzed reaction behavior of 1-silylcyclopropylmethanols

Treatment of 1-silylcyclopropylmethanols with TsOH in methanol gives different homoallyl ethers depending upon the configuration of substituents on cyclopropane ring and the kinds of substituents on carbinyl carbon. Especially, the reaction of cyclopropylmethanols having no substituents on the same side with silyl group on cyclopropane ring proceeds to give the corresponding E-homoallyl ethers with high stereoselectivity. The following protiodesilylation of resulting homoallyl ethers proceeds with retention of configuration.