Regio- and Stereodivergent Allylic Reductions of Bicyclic Piperidine Enecarbamate Derivatives.

The particular nature of tetrahydropyrido[4,3-e]-1,4,2-dioxazines of type 1 allows the regio- and stereoselective obtainment of substituted N-carbamoyl tetrahydropyridines by common reducing agents. A completely novel, biologically active, bicyclic 1,3-diaza-4-oxa-[3.3.1]-nonene scaffold can be generated by the use of lithium triethylborohydride through unprecedented cascade syn-S(N)2' reduction/carbamate reduction/cyclization reactions. The remarkable regioselectivity switches in the allylic reduction process have been rationalized with the aid of computational studies.