Synthesis of eleven-membered carbocycles via a homo-Cope type of five-carbon ring expansion reaction utilized β-(hydroxymethyl)allylsilane

Abstract

Eleven-membered carbocycles were synthesized from six-membered compounds fitted with a β-(hydroxymethyl)allylsilane unit via the title reaction. Namely, trans- and cis-( E)-2-(trimethylsilylmethyl)-3-(2-vinylcyclohex-1-yl)prop-2-en-1-ol were treated with Tf 2O in CH 2Cl 2 in the presence of 2,6-lutidine to afford (1 E)-3-methylenecycloundeca-1,6-diene in good yield. The geometry of the product was shown to depend upon the trans- and cis-substitution pattern on the cyclohexane ring of the substrates; i.e. trans-isomer afforded (6 E)-product exclusively and cis-isomer afforded the mixture of (6 E)- and (6 Z)-product in 1:2 ratio. The ( Z)-substrate with respect to allylsilane moiety afforded the same ring expansion product, however, the yield was lower than the reaction with the ( E)-substrate. The substrates bearing t-butyl or benzyloxy substituents on the cyclohexane ring also afforded the product analogously, indicating that the reaction depends upon the conformation of the substrate. On the other hand, the substrate bearing isopropenyl group instead of a simple vinyl group did not afford the ring expansion product but produced bicyclo[5.4.0]undecane via the ene reaction.