Borohydride reduction 1,3-thiazines

The reduction of dihydro-1,4-thiazines to tetrahydro forms is achieved by the action of a variety of reagents including formic acid, hydrogen sulfide, sodium borohydride and lithium aluminum hydride. The last is particularly useful for the reduction of carbonyl derivatives, although in the case of the amide (105) only partial reduction is effected, leading in due course to the thiazine (106), the hydroxyethyl side chain of which then cyclizes to position 5 of the ring to yield the bicyclic product (107 Scheme 45) (66CPB742). 

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