Scheme 2.

Preparation of vinyl stannane 2. Reagents and conditions: a) TBSO(CH₂)₄MgBr, THF, −78 °C, 88 %; b) LiHMDS, THF; Comins reagent, −78→−20 °C, 82 %; c) (MeBO)₃, [Pd(PPh₃)₄] (10 mol %), K₂CO₃, dioxane, 50 °C, 96 % (>20:1 E/Z); d) DDQ, pH 7 buffer, CH₂Cl₂, 84 %; e) DMP, NaHCO₃, CH₂Cl₂, 82 %; f) (R)-7, c-Hex₂BCl, Et₃N, Et₂O, −78→−20 °C, 96 % (d.r.>20:1); g) TMSCl, imid, CH₂Cl₂, 96 %; h) LiC=CTMS, THF, −78 °C; i) K₂CO₃, MeOH; j) NaIO₄/SiO₂, CH₂Cl₂, 69 % over 3 steps; k) NaI, AcOH, THF, 81 % (8:1 Z/E); l) Me₄NBH(OAc)₃, MeCN, AcOH (3:1), −30 °C, 97 % (d.r.>20:1); m) Me₂C(OMe)₂, PPTS, CH₂Cl₂, 99 %; n) tBuLi, Bu₃SnCl, Et₂O, −78 °C, 81 %. Comins reagent=2-(Tf₂N)-5-Cl(C₅H₃N), DDQ=2,3-dichloro-5,6-dicyano-1,4-benzoquinone, DMP=Dess–Martin periodinane, HMDS=hexamethyldisilazide, PPTS=pyridinium para-toluenesulfonate.