摘要：

The aldol reaction of (o-alkoxyacetophenone)chromium complexes with boron enolates gave predominantly one diastereomeric product as a result of attack at the re-face of the aldehydes. The selectivity of the aldol reactions was remarkably dependent on the ortho substituents of the acetophenone complexes and the ligands on the chromium metal. In the case of the o-methoxy substituent, high diastereoselectivity in the boron enolate aldol condensation was achieved. (o-Methoxyacetophenone)Cr(CO)3 exists in an anti form with respect to the methoxy and the carbonyl oxygen; thus, the corresponding anti boron enolate was formed via coordination of the boron with the benzylic carbonyl oxygen. The resulting anti boron enolate attacked the re-face of the aldehydes through a six-membered cyclic twist-boat transition state. The diastereoselective aldol condensations provide a new method for remote stereocontrol at the 1,5-position of the side chain in optically active forms, combined with stereoselective alkylation of chromium-complexed benzylic ketones.

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