Journal of the American Chemical Society p. 3622 - 3628 (1988)
Update date:2022-08-03
Topics:
Swartz, James E.
Mahachi, Tendai J.
Kariv-Miller, Essie
The mechanism of dimethylpyrrolidinium (DMP(+1)) mediation of the reductive cyclization of 6-hepten-2-one at a mercury electrode was studied.The initial step of the reduction involves formation of a solid composite, (DMP)Hg5, which then transfers an electron to the ketone, regenerating DMP(1+) and Hgo.The ketyl radical anion cyclizes to form a primary alkyl radical, which can either abstract a hydrogen atom from the solvent, dimethylformamide, or be reduced to the corresponding carbanion.Protonation gives 1,2-dimethylcyclopentanol.Both direct and DMP(1+)-mediated reductions of 7-octen-2-one, 5-phenyl-2-pentanone, and 6-heptyn-2-one were studied.All three compounds give cyclic alcohols when the reduction is mediated by DMP(1+).The former two compounds give the corresponding straight-chain alcohols when reduced directly.The latter gives the same cyclized product upon both direct or DMP(1+)-mediated reduction.Redox catalysis studies show that DMP(1+) is a remarkably effective catalysts for the reduction of ketones.The effectiveness of the catalysis correlates with the expected rates of cyclization of the unsaturated ketones and is consistent with a mechanism involving mediation by solid (DMP)Hg5.Redox catalysis studies of the reduction of cyclohexanones indicate that DMP(1+)-mediated reductions are accelerated by increasing
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