12'thioacetal group may either remain intact (route a) or undergo a further coupling process (route b). The selectivity of these routes depends on the relative position of this sulfur moiety to the first double bond thus produced. In other words, when the olefin moiety is formed in a relatively “remote” position, no “interaction” between this double bond and the sulfur group would occur. The reaction would stop at this stage to give an olefin-dithioacetal (route a). ...
