Cyclopropyl Building Blocks for Organic Synthesis,Part 100. Advanced Syntheses of Cyclopropylideneacetates –Versatile Multifunctional Building Blocks for Organic Synthesis

A well reproducible and inexpensive preparation of the cyclopropylideneacetates 2 – 4 has been developed. The key intermediate 2‐(1′‐mesyloxycyclopropyl)acetic acid ( 8 ), produced either from methyl phenylacetate ( 1 ) or 3,3‐dimethoxypropionate ( 5 ‐Me) and 3,3‐diethoxypropionate ( 5 ‐Et) in a sequence of Kulinkovich reductive cyclopropanation, mesylation and oxidative cleavage or cleavage and oxidation, respectively, was either converted to the benzyl ester 11b , or chlorinated (brominated) via the in situ formed acid chloride. The α‐chloro‐ 12a and α‐bromo ester 12b were dehydromesylated by treatment with triethylamine to furnish methyl 2‐chloro‐2‐cyclopropylideneacetate ( 3 ‐Me) and the 2‐bromo analogue 4 ‐Me with an overall yield of 68% (65%, 68%) and 52% (49%, 51%) respectively, starting from 1 ( 5 ‐Me, 5 ‐Et). The parent benzyl cyclopropylideneacetate 2 ‐Bn was obtained by dehydromesylation of 11b with potassium t‐butoxide in t‐butyl methyl ether with an overall yield of 60% (57%, 9%) from 1 ( 5 ‐Me, 5 ‐Et).