BINOL-Ti-Catalyzed Carbonyl-Ene Cyclization by Tuning the 6-Br-Ligand for the Synthesis of 2-Methyl-19-nor-22-oxa Vitamin D Analogue with Significant Differentiation Activity - Mikami, Koichi; Koizumi, Yurika; Osawa, Ayako; Terada, Masahiro; Takayama, Hiroaki; Nakagawa, Kimie; Okano, Toshio (Synlett, 1999)