Free radical and ionic reactions of (Benzoylmethyl)mercurials

Kulkarni, Shekhar
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New reactions of the electrophilic benzoylmethyl radical (PhCOCH[subscript]2·) generated from the corresponding mercurial have been discovered. S[subscript] RN-type reactions have been demonstrated with electron-rich neutral substrates such as trialkyl phosphites, N-methyl pyrrole and N-morpholino-1-cyclohexene. In case of trialkyl phosphites photostimulated reactions in aprotic solvents give [beta]-keto phosphonates via electron transfer from the intermediate phosphoranyl radical to the mercurial. In the dark and in protic solvents ionic reactions predominate due to the complexation of the phosphites with the mercurial and a variety of products are observed. Reaction with N-methylpyrrole gives the 2-benzoylmethyl substituted product while with N-morpholino-1-cyclohexene benzoylmethyl-substituted enamine is observed which on aqueous acid hydrolysis gives the 1,4-dicarbonyl compound in good yield. These reactions involve easily oxidizable adduct radicals of the type ·C(R[subscript]2)-NR[subscript]2, which transfer an electron to the mercurial and continue the chain reaction. Reactions of benzoylmethyl radical with simple alkenes such as cyclohexene, 1-hexene, 1-decene and norbornene give [alpha]-tetralones by cyclization of the adduct radical with the aromatic ring. There seems to be little evidence for a chain reaction or for the loss of a proton from the intermediate cyclohexadienyl radical. Competive cyclization studies carried out with aromatic alkenes showed that formation of a six-membered ring is favored over a five-membered ring. Reactions of [alpha]-carbonyl substituted radicals with simple and electron-rich alkenes carried out in presence of disulfides give products resulting from the trapping of the adduct radicals by the disulfide in good yields. Simple alkenes give [gamma]-alkyl or arylthio carbonyl compounds while enol ethers and vinyl sulfides give 1,4-dicarbonyl compounds after hydrolysis. Stereoselective reactions were observed with dihydropyran. These reactions proceed by a non-chain process and yields are greatly improved when a base such as Li[subscript]2CO[subscript]3 is used.

Chemistry, Organic chemistry