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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 23, Number 9
BKCSDE 23(9)
September 20, 2002 

Photoaddition Reactions of Silyl Ketene Acetals with Aromatic Carbonyl Compounds:A New Procedure for β-hydroxyester Synthesis
Ung Chan Yoon, Moon Jung Kim, Jae Joon Moon, Sun Wha Oh, Hyun Jin Kim, Patrick S. Mariano
Photoaddition reaction, Silyl ketene acetals, Aromatic carbonyl compound, b-Hydroxyester, Single electron transfer photochemistry
Photochemical reactions of aromatic carbonyl compounds with silyl ketene acetals have been explored. Irradiation of acetonitrile or benzene solutions containing aryl aldehydes or ketones in the presence of silyl ketene acetals is observed to promote formation of β-hydroxyester, 2,2-dioxyoxetane and 3,3-dioxyoxetane products. The ratios of these photoproducts, which arise by competitive single electron transfer (SET) and classical Paterno-Buchi mechanistic pathways, is found to be dependent on the degree of methyl-substitution on the vinyl moieties of the ketene acetals in a manner which reflects expected alkyl substituent effects on the oxidation potentials of these electron rich donors. An analysis of the product distribution arising by irradiation of a solution containing butyrophenone (6) and the silyl ketene acetal 9, derived from methyl isobutyrate, provides an estimate of the rate constants for the competitive Norrish type Ⅱ, SET and Paterno-Buchi processes occuring. Finally, sequences involving silyl ketene acetal-aryl aldehyde or ketone photoaddition followed by 2,2-dioxyoxetane hydrolysis represent useful procedures for Claisen-condensation type, β-hydroxyester synthesis.
1218 - 1228
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