CYCLOPROPYL BUILDING-BLOCKS FOR ORGANIC-SYNTHESIS .36. UNPRECEDENTED ADDITION OF DIALKOXYCARBENES TO TETRASUBSTITUTED ALKENES - BICYCLOPROPYLIDENE AND 2-CHLOROCYCLOPROPYLIDENEACETATE

The cycloaddition reactions of several dialkoxycarbenes generated in s itu from the corresponding 2,2-dialkoxy-Delta(3)-1,3,4-oxadiazolines o f the type 3 with bicyclopropylidene 1 afford the dialkyl acetals of d ispiro[2.0.2.1]heptane-7-one (4), the analogous addition to methyl (1- chloromethylene-1-carboxylate)cyclopropane 26 leads to the formation o f a complex mixture of products. Those products can best be rationaliz ed in terms of nucleophilic attack of the dialkoxycarbene on the strai ned CC double bond, to form a dipolar intermediate capable of a variet y of intramolecular rearrangements. Several chemical transformations o f the com pounds of type 4 are reported.