Cyclopropyl building blocks for organic synthesis, 38 -: Highly functionalized bicyclo[3.2.1]octane derivatives from readily available 2′-alkoxytricyclo[3.2.1.02,7]octanes:: Building blocks for terpenes, Part I

2'-Alkoxytricyclo[3.2.1.0(2,7)]octanes 4-R are obtained in good to excellent yields from methyl 2-chloro-2-cyclopropylideneacetate (3) and the dienolates derived from the 3-alkoxycyclohex-2-enones 1-R and 2-R, by a cascade of two consecutive Michael additions and a gamma-elimination. Compounds 4-R are transformed to the correspondingly substituted bicycle[3.2.1]octanecarboxylates 5 by treatment with acid. 2'-Methoxytricyclooctanes 4a-d-Me are readily deprotonated to give chelation-stabilized cyclopropyllithium derivatives 6-Me, which react with electrophiles to yield the 7'-substituted tricyclo[3.2.1.0(2,7)]octanes 4f-i-Me (61-66%). By acidic workup of such reaction mixtures, or subsequent treatment of the isolated products 4f-i-Me with acid, efficient transformation to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 is observed.