Tether-enforced reversal of regioselectivity: head-to-head [4 + 4] photocycloaddition of 2-pyridones
Abstract
Symmetric 3,3′-attachment of a three-atom chain between two pyridones overrides the head-to-tail regioselectivity found in intermolecular photodimerization reactions and gives a nearly quantitative yield of the head-to-head [4 + 4] cycloadduct containing contiguous quaternary centres.