Chemistry

Pocketing the Differences

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Science  25 Aug 2000:
Vol. 289, Issue 5483, pp. 1259
DOI: 10.1126/science.289.5483.1259c

Many compounds contain a carbonyl group (C=O) that is connected to a carbon-carbon double bond (C=C) by an intervening C-C single bond, and derivatizing such α,β-unsaturated compounds selectively is an important synthetic goal. Saito et al. report a general route in which molecular recognition of such compounds by aluminum tris(2,6-diphenylphenoxide), or ATPH, supports alkylation exclusively at the γ-carbons. The alkylation reaction was regioselective, too; addition of benzaldehyde occurred primarily to one side of the C=C bonds in methyl 3-methyl-2-butenoate (1) and to the other side in senecialdehyde. Why opposite sides are favored is revealed by x-ray crystallography of complexes formed by ATPH with the target compounds—the pocket formed by ATPH better accommodates one of the isomers obtained by rotation about the intervening C-C single bond. Several other aspects of the reaction also come under the control as a consequence of complexation of the reactants with ATPH. — PDS

J. Am. Chem. Soc., in press.

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