N-Acyl-2-benzoxazolinones in titanium-mediated aldol reactions

N-Acyl-2-benzoxazolinones readily form trichlorotitanium enolates that react rapidly with aldehydes to provide crystalline syn-aldol adducts in high yield. The resulting products are simply converted to amides, esters, and thioesters. A simple, economical synthesis of 3-hydroxy-2-methylpentanoate N-propionylcysteamine thioesters based on these findings is presented.