Synthesis of the Nakanishi Ring-Locked Retinoid

Scheme 2

Reagents and conditions: (a) KOtBu, 18-crown-6, CH₂Cl₂, r.t., 5 h, and 35%; (b) (i) TBAF, THF, 0°C, and 4.5 h; (ii) MnO₂, CH₂Cl₂, −20°C to 0°C, 2 h, and 47%; (c) NaH, (EtO)₂P(O)CH₂CN, THF, r.t., 3 h, and 99%; (d) (i) DIBAL-H, Et₂O, −78°C to r.t., and 30 min; (ii) SiO₂ gel, ether, and E/Z 96%.