A Simple and Novel Approach To Delineating Stereochemistry of Electrocyclic Reactions

The dynamic stereochemistry of electrocyclic reactions (a class of pericyclic reactions) stems from the operation of either conrotatory (con) or disrotatory (dis) mode of ring-closing and ring-opening processes. Difficulty is often encountered in depicting product stereochemistry resulting from such movements of substituents. A novel, simple, straightforward, and quick approach to delineating product stereochemistry of such reactions is presented. In this approach, the stereochemical properties of reactant and product in electrocyclic reactions are classified as either syn (S) or anti (A). The two substituents at the ends of conjugated polyene system or σ bond of cyclic system in reactant or product are designated as S or A. The product stereochemistry is then delineated as follows: reactant stereochemistry × mode = product stereochemistry, resulting in S × con = S; A × con = A; S × dis = A; and A × dis = S. The procedure is illustrated with several examples of electrocyclic and related pericyclic reactions that are appropriate for an upper-level undergraduate or first-year master’s level organic chemistry course.