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In the presence of 20 mol% of a chiral (acyloxy)borane (CAB) complex prepared from BH3·THF and a chiral mono-O-acylated tartaric acid, achiral silyl enol ethers or ketene silyl acetals react with achiral aldehydes to afford the corresponding aldol-type adducts in good yields with high enantio- and diastereoselectivities. Furthermore, the reactivity of aldol-type reactions can be improved without reducing the enantioselectivity by use of 10—20 mol% of the CAB complex prepared from 3,5-bis(trifluoromethyl)phenylboronic acid and chiral tartaric acid derivative. The enantioselectivity can also be improved without reducing the chemical yield by use of 20 mol% of the CAB complex prepared from o-phenoxyphenylboronic acid and chiral tartaric acid derivative. The observed erythro selectivities and re-face attack of nucleophiles on carbonyl carbon of aldehydes imply that the extended transition state model is applicable.

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Catalytic Asymmetric Aldol-Type Reactions Using a Chiral (Acyloxy) borane Complex. -Condensation of achiral aldehydes with achiral ketene silyl acetals ( cf. (II), 26 examples) or ketone silyl ethers (cf. (IV), 10 examples) promoted by chiral (acyloxy)borane complexes as Lewis acid catalysts affords the corresponding aldol-type adducts in good yields and high enantio-and erythro-diastereoselection under mild experimental conditions. -(ISHIHARA, K.; MARUYAMA, T.; MOURI, M.; GAO, Q.; FURUTA, K.; YAMAMOTO, H.; Bull. Chem.

Bei der photochemischen Reaktion von Benzophenon (I) in Wasser mit einer Hochdruck‐Quecksilberlampe unter Stickstoff erhält man Benzopinakol (II) sowie 2‐ und 4‐Hydroxy‐benzophenon (III).