By heating with iron powder a t 120-150" some y-bromo-a,@-unsaturated carboxylic methyl esters, and, less smothly, the corresponding acids, were lactonized to dz-butenolides with elimination of methyl bromide. The following conversions have thus been made : methyl y-bromocrotonate (1 c) and the corresponding acid (1 d) to d"-butenolide @a), methyl y-bromotiglate (3c) and the corresponding acid (3d) to u-methyl-da-butenolide (8b). a mixture of methyl transand cis-y-bromosenecioate (7c and 7e) and a mixture of the corresponding acids (7d and 7f) to 8methyl-da-butenolide (8c). The procedure did not work with methyl trans-y-bromo-Am-pentenoate (512) nor with its acid (5d).Most of the y-bromo-u,j%unsaturated carboxylic esters ( l c , 7 c , 7e and 5 c ) are available by direct N-bromosuccinimide bromination of the =,@-unsaturated esters 1 a, 7a and 5a; methyl ybromotiglate (3c) is obtained from both methyl tiglate (3a) and methyl angelate (4a), but has to be separated from a structural isomer. The y-bromo-u, /&unsaturated esters are shown by NMR. to have the indicated configurations which are independent of the configuration of the a,@-unsaturl)

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