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[126.96.36.199]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.