Figure 6: Synthesis of the lactone 20.
From: Biomimetically inspired asymmetric total synthesis of (+)-19-dehydroxyl arisandilactone A
(a) Grignard reagent (1.5 eq), THF, rt; (b) Hoveyda-Grubbs II (17, 0.05 eq), PhMe, 80 °C, 79% in two steps; (c) Ac2O (2.0 eq), DMAP (0.5 eq), Et3N (5.0 eq), DCM, rt, 97%; (d) LiHMDS (2.5 eq), CF3CO2CH2CF3 (1.5 eq), THF, −78 °C to 0 °C. (e) TsN3 (1.4 eq), Et3N (3.0 eq), MeCN, rt, 93% in two steps; (f) Cu(tbs)2 (0.1 eq), PhMe, 80 °C, 4.5 h, 65%. ; Cu(tbs)2, bis(N-tert-butylsalicylaldiminato) copper(II); DMAP, 4-dimethylaminopyridine; TsN3, tosylazide.
