[Br:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[O:8][CH2:7][CH2:6][C:5]2=O.[BH4-].[Na+].CC1C=CC(S(O)(=O)=[O:23])=CC=1.BrC1C=C2C(=CC=1)OCC=C2.C[N+]1([O-])CCOCC1>O=[Os](=O)(=O)=O.O.CC(C)=O.CC(O)(C)C>[Br:1][C:2]1[CH:3]=[C:4]2[C:9](=[CH:10][CH:11]=1)[O:8][CH2:7][C:6](=[O:23])[CH2:5]2The starting material 6-bromochroman-3-one (5A) was prepared from 6-bromochroman-4-one in a manner similar to that described in the literature (Synthesis, 1980, 621): 6-bromochroman-4-one was reduced with NaBH4 (1.2 eq, MeOH-DCM, 0° C. to RT, 2 h) and then eliminated with pTsOH (cat., toluene, reflux, 3 h, 90% for 2-steps). The resulting 6-bromochromene was subjected to osmylation (cat. OsO4, 1 eq. NMO, water-acetone-tBuOH, RT, overnight) and subsequent treatment with pTsOH (cat., toluene, reflux, 15 min, 86% for 2-steps) to provide 6-bromochroman-3-one (5A).
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