Deoxygenation without ring reduction

The reduction of furoxans and benzofuroxans has been reviewed in detail in CHEC(1984) and CHEC-II(1996). The main reducing agents to remove oxygen atoms from nitrogen without cleavage of the heterocyclic ring are phosphines and phosphites. These reactions, namely deoxygenation of furoxans and benzofuroxans, are discussed in Section 5.05.4.2.2. 

Chemical reduction of azine //-oxides, depending on substrate structure, reductant and reaction conditions can proceed both with or without deoxygenation of the N-atom. Thus, 1,2,3-triazine 1-oxide (337) with NaBH4 gives 2,5-dihydro-1,2,3-triazine (336), suggesting that the N-oxide moiety back-donates electrons to the triazine ring. On the other hand, on reduction of the isomeric 2-oxide leading to tetrahydro derivatives (338) and (339) the N-oxide function is not touched (82H(17)317). 

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