Thiophene S-oxides 4 have been shown to undergo [4+2] cycloadditions with m
ethylenecyclopropanes 2 with one or two electron acceptor substituents, i.e
. even the tetrasubstituted 2-chloro-2-cyclopropylideneacetate 2c reacted w
ell. However, for the tetrasubstituted alkene bi(cyclopropylidene) 2f high
pressure had to be applied to make it react with 4. Only one diastereoisome
r was formed in all the reactions. X-Ray crystal structure analyses of two
of the cycloadducts, 3a and 3f, have been performed, their relative configu
ration determined as being endo,syn. The Wittig olefination of cyclopropano
ne hemiacetal to generate the methylenecyclopropanes and the subsequent cyc
loaddition can be carried out in a one-pot operation. This procedure is one
of many potential one-pot or multi-component reactions involving stabilize
d phosphoranes. A further example of this type of reaction is shown in the
novel desilylation-Wittig olefination of 1-ethoxy-1-trimethylsilyloxycyclop
ropane 5 to yield in one step cyclopropylideneacetates, e.g. 2a.