O-alkoxy phenyl ketones

The photocyclization of o-alkoxy phenyl ketones to yield benzofuranols (57 and 58) represents one of the earliest example of 8-H-abstraction from the lowest n, n triplet Wagner et al. [18] have provided detailed photokinetic data studying the photocyclization of a variety of o-alkoxyphenyl ketones 56, and have revealed that quantum efficiency for cyclization for 56d was the lowest (0.023) and that for 56f the highest (1.00). The diastereoselectivity for cyclization of 56 was found to be higher in benzene and lower in polar solvents. From the estimated kH values (0.6-25 x 106 s 1), it was inferred that the low rate constant for 56e (8 x 106 s ) compared to that for 56g (25 x 106s 1) i s due to the alkyl chain in the alkoxy groups that points away from the o-carbonyl moiety in the most populated equilibrium conformations (Table 8.1). 

B.-S. (1990) The photocyclization of o-alkoxy phenyl ketones. Journal of the American Chemical Society, 112, 5199-5211. 

Dimethyl(phenyl)silane reduces aldehyde and ketone carbonyls with the aid of fluoride ion or acid. a-Acylpropionamides, 1-aminoethyl ketones, and 1-alkoxyethyl ketones are readily converted into the corresponding -hydroxy amides, o -amino alcohols, and a-alkoxy alcohols, respectively. The stereoselectivity is complementary and generally high erythro (or syn) isomers are obtained with trifluoroacetic acid (TFA), whereas threo (or anti) isomers are obtained with fluoride ion activator (eq 1). The erythro selectivity in the acid-promoted carbonyl reduction is ascribed to a proton-bridged Cram s cyclic transition state. On the other hand, the threo selectivity in the fluoride-mediated reduction is explained in terms of the Felkin-Anh t) e model, wherein a penta-or hexacoordinated fluorosilicate is involved. No epimerization at the chiral center is observed during the reaction. 

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