Bonds reductive cleavage

The dynamics of carbon-halogen bond reductive cleavage in alkyl halides was studied by MP3 ab initio calculations, using pseudopotentials for the halogens and semidiffuse functions for the heavy atoms [104], The effect of solvent was treated by means of the ellipsoidal cavity dielectric continuum model. Both a concerted (i.e., a one-step) and a stepwise mechanism (in which an anion radical is formed at first) were... 

Bertran, J., Gallardo, I., Moreno, M. and Saveant, J. M. Dissociative electron transfer. Ab initio study of the carbon-halogen bond reductive cleavage in methyl and perfluoromethyl halides. Role of the solvent, JAm.Chem.Soc., 114 (1992), 9576-9583... 

With an ot, y-ketodiol, cyclization to produce a 3-furanone derivative is feasible, as is shown for the synthesis of ascofuranone (71) and geiparvarin (72) (Scheme 6.57) (286). The precursor for 71 was prepared by the cycloaddition of diene 66 to nitroalcohol 67. In this case, regioselective attack occurred only on the terminal double bond. Reductive cleavage-hydrolysis of the isoxazoline adduct 68 with Mo(CO)6 followed by acid-induced cyclization led to the furanone intermediate (286). A similar strategy was used for the synthesis of geiparvarin (72) (Scheme 6.58) (286). 

Other typical reactions of acidic hydrocarbons with alkali metals are given in Table 1. Example 4 (Table 1) shows that, in addition to hydrogenation of multiple bonds, reductive cleavage may be a complicating side reaction. In the reaction of triphenylmeth-ane this side reaction may be eliminated by addition of butadiene which, as its radical anion, acts as proton acceptor. 

The racemic dilithio species 69 was prepared from l-(l,3-dithian-2-yl)pro-pan-l-ol and added to nitrone 62 to provide hydroxylamine 70, which was then subjected to Cope-House pericychc cyclization, installing the methyl substituent at the C-5 position (Scheme 14). The resulting pyrrolizidine AT-oxides 71-72, obtained as a 1 1 mixture in a moderate 55% yield, were submitted to subsequent N—O bond reductive cleavage, providing the desired pyrrolizidines 73-74. A two-step sequence involving hydrolysis of the dithio-ketal and then reduction of the ketone provided the partially protected hya-cinthacine core as a single isomer in 33% yield. Subsequent removal of the... 

Isse AA, Gennaro A, Lin CY, Hodgson JL, Coote ML, Guhashvili T. Mechanism of carbon-halogen bond reductive cleavage in activated alkyl halide initiators relevant to living radical polymerization theoretical and experimental study. J Am Chem Soc 2011 133 6254-6264. 

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