Regio- and stereoselectivity in light-induced [4 + 2]- and [2+ 2]-cycloadditions of alpha-cyanoenamines to aromatic carbonyl compounds and hydrocarbons

摘要

alpha-Cyanoenamines with varied saturated azaheterocyclic amino groups are added to triplet excited 1-acylnaphthalenes in a highly regio-, stereo- and diastereo-selective manner forming l,4-dihydro-l,4-ethanonaphthalenes in a [4 + 2]-mode. Replacementof the heterocyclic donor groups in the title compounds by open chain dialkylamino groups virtually eliminates the stereoselectivity in the [4 + 2]-addi-tion. The latter reaction may be preceded and/or accompanied by an independent and both regio- and stereoselective [2 + 2]-addition. Similar striking selectivity phenomena are observed in the oxetane formation from aromatic 1,2-diketones and a-cyanoenamines, [2 + 2]-Photoadditions of the latter to naphthalene, phenan-threne, anthracene and acenaphthylene display reduced regio-, stereo- and dias-tereoselectivity in the cases studied at satisfactory preparative yields. These additions seem to be controlled by preferred singlet exciplex geometries.