Single electron reduction of carbonyls provides a powerful strategy to access ketyl species, which are utilized to couple electrophiles and provide unique construction of C-C bonds, inaccessible via typical two electron pathways. While many complex molecules have been designed utilizing these ketyl couplings, they require harsh reductants to overcome the high reduction potential of carbonyls (Ep,c &gt; –2.0 V), limiting the synthetic utility of ketyl transformations. In hopes to obviate the necessity of strong reductants, we developed an in situ activation strategy with simple acyl halides to convert aldehydes to a-oxy iodides (Ep,c –1.1 V). The donation of the oxygen lone pairs into the C-I bond (n→σ*) significantly lower the reduction potential (D 1200 mV), allowing for a more facile reduction. Employing this aldehyde activation strategy, a reductive intermolecular aza-pinacol coupling was achieved avoiding the use of strong reductants (Sm, Ti, Na, etc.) and precludes the formation of homo-coupling product. Access of ketyl radicals and subsequent catalyst turnover was achieved utilizing divergent electron transfer and atom transfer pathways to generate amino alcohols utilizing mild reductants.

Reductive ketyl radical couplings via atom transfer catalysis

2019 Spring National Meeting

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