Abstract
โThree alkyltitanium reagents of RTi(OโiโPr)~3~ (R = Cy (1a), iโBu (1b), and nโBu (1c)) were prepared in good yields. The highโresolution mass spectroscopy showed that 1b and 1c in the gas phase are monomeric species. However, the solid state of 1a revealed a dimeric structure. Asymmetric additions of 1a, 1b, 1c to aldehydes catalyzed by a titanium catalyst of (R)โH~8~โBINOL were studied at room temperature. The reactions produced desired secondary alcohols in good yields with good to excellent enantioselectivities of up to 94% ee. Reactivity and enantioselectivity differences, in terms of steric bulkiness of the R nucleophiles, are herein described. The addition reactions of secondary cโhexyl to aldehydes were slower than the reactions of primary iโbutyl or nโbutyl nucleophiles. For the primary alkyls, lower enantioselectivities were obtained for products from addition reactions of the linear nโbutyl as compared with the enantioselectivities of products from the addition reactions of the branched iโbutyl group. The same stereochemistry of RTi(OโiโPr)~3~ addition reactions as the addition reactions of organozinc, organoaluminum, Grignard, or organolithium reagents directly supports the argument of that titaniumโcatalyzed addition reactions of aldehydes involve an addition of an organotitanium nucleophile. Chirality, 2011. ยฉ 2011 WileyโLiss, Inc.