Chemistry of chelate-type hypervalent boron and aluminum : Utilization for selective organic synthesis

Abstract

In this review, the hypercoordination of boron and aluminum as typical main group elements is embodied, and their synthetic utility is demonstrated with several synthetic examples. B and Al Lewis acids are found to be successfully utilized in several chelation-controlled reactions of various substrates (alkoxy carbonyl compounds, fluoro carbonyl compounds, fluoro epoxides, and alkoxy epoxides) via unprecedented pentacoordinate chelate-type complex formation by taking advantage of the exceedingly high affinity of B and Al to fluorine and oxygen, and hence, contrary to the previous observations, can be classified as chelating Lewis acid reagents rather than non-chelating Lewis acids. In addition to the experimental demonstration, such pentacoordinate complex formation of B and Al Lewis acids with various bidentate substrates is also characterized by low-temperature 1H, 13C, 11B, 27Al NMR spectroscopy.