[CH3:1][C:2]1([CH3:13])[C@H:7]2[C@@H:3]1[C@H:4]([C:9](Br)([Br:11])[Br:10])[O:5][C:6]2=[O:8].CC1(C)[C@H]2[C@@H]1[C@@H](C(Br)(Br)Br)OC2=O.C(=O)([O-])O.[Na+].C([O-])=O.[Na+].Cl>CO>[Br:10][C:9]([Br:11])=[CH:4][C@H:3]1[C@@H:7]([C:6]([OH:8])=[O:5])[C:2]1([CH3:1])[CH3:13]A mixture of (1R,4R,5S)-6,6-dimethyl-4-(tribromomethyl)-3-oxabicyclo[3.1.0]hexan-2-one (I, R1=X1=X2=Br) and (1R,4S,5S)-6,6-dimethyl-4-(tribromomethyl)-3-oxabicyclo[3.1.0]hexan-2-one (I, R1=X1=X2=Br), 0.38 g (0.001 mol), is stirred with sodium hydrogen carbonate, 0.126 g (0.0015 mol), sodium formate, 0.27 g (0.004 mol), and Pt(C) 5%, 0.03 g, in about 4 ml of methanol at 50° C. for 5.5 hours. The reaction mixture is acidified with aqueous hydrochloric acid and extracted twice with methyl t-butyl ether which is dried and evaporated. There is obtained 0.28 g of purity 61% (GC, area-%). The retention time is identical to that of II prepared according to Ref.6, and MS (Mass (intensity in % of base peak): 296 (5) M+, 298 (9) (M+2)+, 300 (4) (M+4)+, 255 (24), 253 (45), 251 (23), 219 (100), 217 (98), 201 (18), 199 (22), 197 (13), 174 (29), 172 (33)) is identical to MS of II prepared according to Ref.6.
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