Cyclopropyl building blocks for organic synthesis. Part 36. Unprecedented addition of dialkoxy carbenes to tetrasubstituted alkenes: bicyclopropylidene and 2-chlorocyclopropylideneacetate.
The cycloaddn. reactions of several dialkoxy carbenes generated in situ from the corresponding dialkoxyoxadiazolines of type I (R = R1 = alkyl) with bicyclopropylidene afford the dialkyl acetals of dispiro[22.214.171.124]heptan-7-one (II), whereas the analog addn. to (1-chloromethylene-1-carboxylate)cyclopropane leads to the formation of a complex mixt. of products. Those products can best be rationalized in terms of nucleophilic attack of the dialkoxy carbene on the strained CC double bond, to form a dipolar intermediate capable of a variety of intramol. rearrangements. Several reactions of the compds. of type II are reported.
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