The methylenation of beta-lactones 5 with dimethyltitanocene provides a ver
satile, reliable, and highly chemoselective entry to 2-methyleneoxetanes 7.
The conversion proceeds selectively in the presence of alkenes, unprotecte
d alcohols, and a variety of other carbonyl moieties, A study of conditions
for the optimization of this reaction is delineated. In addition, the firs
t X-ray structure of a 2-methyleneoxetane, which shows its similarity to re
lated p-lactones, is reported. Reactivity studies of 2-methyleneoxetanes ar
e presented in which it is demonstrated that these compounds are attacked a
t C-4 with a nucleophile; then, subsequently, the resultant enolate reacted
with an electrophile. An interesting dichotomy of reactivity was observed
when methyleneoxetane 7c was treated with electrophiles. Reaction of 7c wit
h acetic acid gave acetoxyoxetane 19. When 7c was exposed to bromine, dibro
moketone 20 resulted.