“…[24] Protection of the secondary alcohol of 5 with SEM (trimethylsilylethoxymethyl), reduction of lactone to lactol with DIBAL-H, Lemieux-Johnson oxidation of terminal olefin to afford lactol with a6 ,5-cisbicyclic skeleton, and PDC (pyridinium dichromate) oxidation of lactol were separately conducted to provide the lactones 4 (rac-4a, rac-4b, rac-4c,a nd rac-4d). [25] Final stereo-diversification was performed by Davis oxidation. [26] Despite the nature 65 equiv), MS4,C H 2 Cl 2 ,RT, 12 h(66 %f or rac-4a over 4steps, 70 %f or rac-4b over 4s teps, 36 %f or rac-4c over 4steps, 56 %for rac-4d over 4s teps);j )KHMDS (potassium bis(trimethylsilyl)amide)( 1.5 equiv), Davis reagent (2.0 equiv), THF, À78 8C, 4h(50 %f or rac-3a,20% for rac-3b,3 1% for rac-3c,4 8% for rac-3d,81% for rac-3e,4%f or rac-3f79 %f or rac-3g); k) Tf 2 O(1.1 equiv), pyridine(2.4 equiv), CH 2 Cl 2 , À40 8C, 4h;l)sodium trifluoroacetate (2.0 equiv), DMF (N,N-dimethylformamide), 60 8C, 2d,t hen MeOH (60 %o ver 2s teps).…”