Temperature- and Reagent-Controlled Complementary Syn- and Anti-Selective Enolboration-Aldolization of Substituted Phenylacetates.

In contrast to methyl phenylacetates, methyl arylacetates do not provide syn-aldols in the dicyclohexylboron triflate/triethylamine (Chx2BOTf/Et3N)-mediated enolboration-aldolization reaction. However, a combination of a less bulky boron reagent (dibutylboron triflate, n-Bu2BOTf), a bulky amine (i-Pr2NEt), and ambient temperature is required to obtain syn-aldols from methyl arylacetates. The corresponding anti-aldol products have been synthesized by the enolboration-aldolization of methyl arylacetates in the presence of Chx2BOTf/Et3N at a lower temperature. We report the first example of a complementary syn- and anti-selective enolboration-aldolization of arylacetates.