Posts Tagged ‘antarafacial’

The stereochemistry of [8+2] pericyclic cycloadditions.

Sunday, July 10th, 2011

Steve Bachrach has blogged on the reaction shown below. If it were a pericyclic cycloaddition, both new bonds would form simultaneously, as shown with the indicated arrow pushing. Ten electrons would be involved, and in theory, the transition state would have 4n+2 aromaticity. In fact Fernandez, Sierra and Torres have reported that they can trap an intermediate zwitterion 2, and in this sense therefore, the reaction is not pericyclic but nucleophilic addition from the imine lone pair to the carbonyl of the ketene (it finds the half way stage convivial). But this got me thinking. Does this reaction have any pericyclic character at all? And if so, could it be enhanced by design?