[BH4-].[Na+].[N:3]1[CH:8]=[CH:7][CH:6]=[C:5]([C:9]2[S@:14](=[O:15])[CH2:13][CH2:12][CH2:11][CH:10]=2)[CH:4]=1.O.CC(C)=O>C(O)C>[N:3]1[CH:8]=[CH:7][CH:6]=[C:5]([C@H:9]2[CH2:10][CH2:11][CH2:12][CH2:13][S@:14]2=[O:15])[CH:4]=1A stirred suspension of sodium borohydride (11.44 g) in ethanol (935 ml) is treated with a solution of crude (R)-6-(3-pyridyl)-3,4-dihydro-2H-thiopyran 1-oxide (116.9 g; prepared as described in Example 10) in ethanol (117 ml) at room temperature under nitrogen. The mixture is stirred for 3 hours and is then treated with water (935 ml) and acetone (93 ml), with cooling. The solution is extracted with dichloromethane (3×800 ml), the combined extracts are washed with aqueous sodium chloride solution (2×800 ml;25% w/v), dried over magnesium sulphate, and evaporated under reduced pressure to give a paste (96.2 g). This paste is recrystallised from a mixture of tert-butyl methyl ether and methyl ethyl ketone, to give (1R,2R)-2-(3-pyridyl)tetrahydro-2H-thiopyran 1 -oxide (36.16 g), in the form of a pale yellow powder, m.p. 121°-126° C., enantiomeric excess 99.6%. [NMR (CDCl3):- 1.6(m, 1H), 1.8(m,2H),2.0(m,1H),2.4(m,1H),2.7(m,2H), 3.2(m,1H),3.5(dd,1H),7.3(m,1H),7.7(dt, 1H), 8.6(m,2H)].
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