Engineering reactions in crystalline solids: Photochemical generation of secondary and tertiary enol radical pairs from crystalline ketodiesters

The photochemical decarbonylation of several crystalline 1,3-acetonedicarbo xylates has been analyzed in solution and in the solid state. It is shown t hat the efficiency of the solid-state reaction depends on the stability of the intermediate acyl-alkyl and alkyl-alkyl radical pairs. Reactions procee ding through tertiary enol radicals are more efficient than reactions proce eding through secondary enol radical centers. Solid-state reactions that re quire the intermediacy of primary enol radicals do not occur. It is also sh own that the selectivity of product formation in crystals depends on the st ructure of the reactant solid phase.