Hydrogen bonding, Paterno-Biichi reaction

Griesbeck, A.G. and Bondock, S. (2001) Paterno-Biichi reactions of allylic alcohols and acetates with aldehydes hydrogen-bond interaction in the excited singlet and triplet states Journal of the American Chemical Society, 123 (25), 6191-6192. 

Hydrogen bonding between the ground-state reactants dihydropyridone (259) and an aldehyde 260 was found to be responsible for a high facial diastereoselectivity (>90% de) (see also Special Topic 6.3) in the Paterno Biichi reaction (Scheme 6.107).900 901 X-ray analysis, furthermore, revealed that the corresponding lactam moieties in the racemic product 261 are intramolecularly hydrogen-bonded (dashed). 

Similarly to carbonyl compounds (Section 6.3.1), thiocarbonyl compounds abstract hydrogen upon irradiation however, both n,7t and n,n excited states are reactive and the hydrogen atom can be added to either the sulfur (Table 6.17, entry 1) or carbon (entry 2) atoms of the C=S bond. Aliphatic and aromatic thiocarbonyl compounds can also undergo photocycloaddition to unsaturated compounds from both singlet or triplet excited states to form thietanes (analogously to the Paterno Biichi reaction see Section 6.3.2) (entry 3) or 1,4-dithianes. On the other hand, fragmentation of the S C bond is a typical primary process observed in excited sulfones and sulfonates (entry 4), followed by efficient SO2 extrusion from the radical intermediate. 

Effect of Hydrogen Bonding on Diastereoselectivity of Paterno-Biichi Reaction... 

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