Pure la, pure 2a, or any mixture of the two results in a similar proportion of 9a and 9c when treated with benzenethiol. This is also the case if dimethyl acetylenedicarboxylate is treated with two or more equivalents of benzenethiol.'As pointed out by Newton et al.'the first addition of thiol to the alkyne is predominantly trans in stereochemistry, but our results do not support their contention that the second addition of the thiol to the resulting olefins is ...
