One pot tandem dual CC and CO bond reductions in the β-alkylation of secondary alcohols with primary alcohols by ruthenium complexes of amido and picolyl functionalized N-heterocyclic carbenes??

Dalton Transactions Pub Date: 2021-09-29 DOI: 10.1039/D1DT02849A

Abstract

Two different classes of ruthenium complexes, namely, [1-mesityl-3-(2,6-Me2-phenylacetamido)-imidazol-2-ylidene]Ru(p-cymene)Cl (1c) and {[1-(pyridin-2-ylmethyl)-3-(2,6-Me2-phenyl)-imidazol-2-ylidene]Ru(p-cymene)Cl}Cl (2c), successfully catalyzed the one-pot tandem alcohol–alcohol coupling reactions of a variety of secondary and primary alcohols, in moderate to good yields of ca. 63–89%. The mechanistic investigation performed on two representative catalytic substrates, 1-phenylethanol and benzyl alcohol using the neutral ruthenium (1c) complex showed that the catalysis proceeded via a partially reduced C[double bond, length as m-dash]C hydrogenated carbonyl species, [PhCOCH2CH2Ph] (3′), to the fully reduced C[double bond, length as m-dash]O and C[double bond, length as m-dash]C hydrogenated secondary alcohol, [PhCH(OH)CH2CH2Ph] (3). Furthermore, the time dependent study showed that the major product of the catalysis modulated between (3′) and (3) during the catalysis run performed over an extended period of 120 hours. Finally, the practical utility of the alcohol–alcohol coupling reaction was demonstrated by preparing five different flavan derivatives (13–17) related to various bioactive flavonoid natural products, in a one-pot tandem fashion.

Graphical abstract: One pot tandem dual C [[double bond, length as m-dash]] C and C [[double bond, length as m-dash]] O bond reductions in the β-alkylation of secondary alcohols with primary alcohols by ruthenium complexes of amido and picolyl functionalized N-heterocyclic carbenes
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