N-bromobutanimide → rac-(7aR,11aS)-2-bromo-11a-ethyl-7,7a,8,10,11,11a-hexahydro-6H-spiro[dibenzo[b,d]oxepine-9,2'-[1,3]dioxolan]-3-amine

Participants

Reaction Steps

A solution of rac-(7aR,11aS)-11a-ethyl-7,7a,8,10,11,11a-hexahydro-6H-spiro[dibenzo[b,d]oxepine-9,2′-[1,3]dioxolan]-3-amine (86, R2=Ethyl) (11.2 g, 37.0 mmol) in THF (370 mL) was cooled to about −10° C. in a salt/ice bath and was then treated with NBS (6.59 g, 37.0 mmol) with stirring for about 5 min. The reaction was quenched by addition of sat. aq. NaHCO3 (250 mL), and the mixture was diluted with EtOAc (350 mL). The aqueous phase was extracted with EtOAc (2×50 mL) and the combined organic phases were washed with brine (350 mL), dried over Na2SO4, filtered, and concentrated under reduced pressure. The crude material was purified on silica gel (220 g, eluted with 0% to 40% EtOAc in heptane). Collection and concentration of the appropriate fractions gave rac-(7aR,11aS)-2-bromo-11a-ethyl-7,7a,8,10,11,11a-hexahydro-6H-spiro[dibenzo[b,d]oxepine-9,2′-[1,3]dioxolan]-3-amine (87, R2=Ethyl) (13.6 g, 96%) containing about 20% of a minor regioisomer. The material was used directly in Step #4 without further purification. LC/MS, method 3, 2.49 min, MS m/z 382, 384 (M+H)+.

Provenance & Evidence