Methyl-2-bromomethylprop-2-enoate reacts with benzaldehyde and with sa
licylaldehyde via its Sn and Zn complexes under aqueous conditions to
form alpha-methylene-gamma-lactones in high yields. In the case of sal
icylaldehyde X-ray analysis proves conclusively formation of a five- r
ather than a seven-membered ring. Under the above conditions 2-bromome
thyl-3-phenylprop-2-enoate does not afford any cyclic products.