- Alcohols as alkylating agents in heteroarene C-H functionalization
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Redox processes and radical intermediates are found in many biochemical processes, including deoxyribonucleotide synthesis and oxidative DNA damage. One of the core principles underlying DNA biosynthesis is the radical-mediated elimination of H2O to deoxygenate ribonucleotides, an example of 'spin-centre shift', during which an alcohol C-O bond is cleaved, resulting in a carbon-centred radical intermediate. Although spin-centre shift is a well-understood biochemical process, it is underused by the synthetic organic chemistry community. We wondered whether it would be possible to take advantage of this naturally occurring process to accomplish mild, non-traditional alkylation reactions using alcohols as radical precursors. Because conventional radical-based alkylation methods require the use of stoichiometric oxidants, increased temperatures or peroxides, a mild protocol using simple and abundant alkylating agents would have considerable use in the synthesis of diversely functionalized pharmacophores. Here we describe the development of a dual catalytic alkylation of heteroarenes, using alcohols as mild alkylating reagents. This method represents the first, to our knowledge, broadly applicable use of unactivated alcohols as latent alkylating reagents, achieved via the successful merger of photoredox and hydrogen atom transfer catalysis. The value of this multi-catalytic protocol has been demonstrated through the late-stage functionalization of the medicinal agents, fasudil and milrinone.
- Jin, Jian,MacMillan, David W. C.
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- Steric and Conformational Effects in Nicotine Chemistry
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The stereoselectivity of iodomethylation of nicotine and seven nicotine analogues having pyridine alkyl groups was determined by using 13C NMR.Alkylation at the pyridine (N) and at the pyrrolidine (N') nitrogens was observed.Two modes of N'-iodomethylation occur, cis and trans to the pyridine ring.N'-Iodomethylation occurs regioselectively cis to the pyridine ring for all compounds examined.The N/N' and N'cis/N'trans ratios for the nicotinoids were evaluated with regard to (1) the orientation of the N'-methyl group in the free base, (2) conformational properties of the pyridine ring with respect to the pyrrolidine ring, and (3) steric hindrance and buttressing effects on the pyridine nitrogen.The Curtin-Hammett principle and the Winstein-Holness equation are used to analyse reactions.
- Seeman, Jeffrey I.,Secor, Henry V.,Chavdarian, Charles G.,Sanders, Edward B.,Bassfield, Ronald L.,Whidby, Jerry F.
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p. 3040 - 3048
(2007/10/02)
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