Radical reduction of aromatic azides to amines with triethylsilane.

Aromatic azides are inert toward triethylsilane under thermal conditions in the presence of a radical initiator, but in the presence of additional catalytic amounts of tert-dodecanethiol, they afford anilinosilanes and thence the corresponding anilines in virtually quantitative yields.

Reaction of azides with dichloroindium hydride: very mild production of amines and pyrrolidin-2-imines through possible indium-aminyl radicals.

Organic azides are easily reduced to the corresponding amines by reaction with dichloroindium hydride under very mild conditions and in a highly chemoselective fashion. Gamma-azidonitriles give rise to outstanding five-membered cyclizations affording pyrrolidin-2-imines. A rationalization of the overall experimental data cannot exclude the occurrence of competitive radical and nonradical pathways, but certain results are, however, soundly consistent with the intermediacy of indium-bound nitrogen-centered radicals.

Generation and cyclization of unsaturated carbamoyl radicals derived from S-4-pentynyl carbamothioates under tin-free conditions.

The radical reaction of benzenethiol with S-4-pentynyl carbamothioates provides a valuable protocol for the tin-free generation of carbamoyl radicals, which arise from intramolecular substitution at sulfur by the initial sulfanylvinyl radicals. This procedure can be usefully employed to achieve N-benzylcarbamoyl radical 5-exo and 4-exo cyclizations leading, respectively, to pyrrolidinones and azetidinones, although, for the latter, it seems of lesser utility. Novel evidence is presented that N-tosyl-substituted carbamoyl radicals display a peculiar tendency to yield the corresponding isocyanate by beta-elimination of the tosyl radical.

Radical reduction of aromatic azides to amines with tributylgermanium hydride.

[reaction: see text] Aromatic azides are inert toward tributylgermanium hydride under thermal conditions in the absence and in the presence of a radical initiator but in the presence of catalytic amounts of benzenethiol undergo fast reaction, yielding reduced anilines and 2-germylated derivatives in high overall yields.

Thermal reactions of tributyltin hydride with alpha-azido esters: unexpected intervention of tin triazene adducts under both nonradical and radical conditions.

Thermal reaction of various alpha-azido esters with Bu(3)SnH in refluxing benzene results in smooth production of 3-(tributylstannyl)-1-triazene adducts affording cyclized 1,2,3-triazol-4-ones in preference to reduced amines and thence provides a new useful method for the preparation of these triazole derivatives. In the presence of AIBN the occurrence of triazene products still remains important or even exclusive and, consequently, generation of the expected stannylaminyl radicals is seriously limited. With 2-azidomalonates and alpha-azido-beta-keto esters stannyltriazenes can similarly occur in the absence of the radical initiator, but in the latter cases the ensuing triazenes undergo preferential cyclization onto the ketone moiety to give reactive hydroxytriazolines.

Cyclizations of N-stannylaminyl radicals onto nitriles.

[reaction: see text] Stannylaminyl radicals derived from radical reactions of Bu(3)SnH with azidoalkylmalononitriles exhibit highly efficient 5- and 6-exo cyclization onto either nitrile group to give aminoiminyl radicals that in turn are reduced to amidines or undergo successive 5-exo cyclization onto an internal alkene.

Cascade radical reactions via alpha-(arylsulfanyl)imidoyl radicals: competitive [4 + 2] and [4 + 1] radical annulations of alkynyl isothiocyanates with aryl radicals.

Aryl radicals react with 2-(2-phenylethynyl)phenyl isothiocyanate through a novel radical cascade reaction entailing formation of alpha-(arylsulfanyl)imidoyl radicals and affording a new class of compounds, i.e. thiochromeno[2,3-b]indoles.

Generation and intramolecular reactivity of acyl radicals from alkynylthiol esters under reducing tin-free conditions.

[reaction: see text] The radical chain reaction of benzenethiol with alkynylthiol esters provides a new, valuable protocol for the tin-free generation of acyl radicals that arise from intramolecular substitution at sulfur by the initial sulfanylvinyl radicals.

Intramolecular cyclization of acyl radicals onto the azido group: a new radical approach to cyclized lactams.

[reaction: see text] Aryl- and alkyl-derived azidoacyl radicals, generated from thiolesters by intramolecular homolytic substitution at the sulfur, can undergo five- and six-membered cyclization onto the azido moiety to give cyclized lactams.

Reactions of Benzocyclic β-Keto Esters with Sulfonyl Azides. 2. Further Insight into the Influence of Azide Structure and Solvent on the Reaction Course.

The reactions of 2-ethoxycarbonyl-1-benzosuberone with 4-methoxybenzenesulfonyl, 2,4,6-triisopropylbenzenesulfonyl, methanesulfonyl, and trifluoromethanesulfonyl azide, in the presence of triethylamine, have been investigated in ,-dimethylformamide, acetonitrile, or tetrahydrofuran with the intent of clarifying the influence of both the azide electrophile and solvent on the reaction course. The present findings, in addition to those previously obtained with tosyl and 4-nitrobenzenesulfonyl azide, indicate that both the electronic features of the sulfonyl azide and the solvent polarity greatly affect the possible occurrence of azidation and/or Favorskii-type ring contraction at the expense of deacylating diazo transfer. Azidation is promoted by the less electrophilic azides, while it is virtually avoided by the more electrophilic ones.