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Keywords:

  • homogeneous catalysis;
  • diastereoselectivity;
  • propargylation;
  • ruthenium;
  • transfer hydrogenation

Abstract

Under the conditions of ruthenium-catalyzed transfer hydrogenation employing isopropanol as a source of hydrogen, isopropoxy-substituted enyne 1 b and aldehydes 3 a3 l engage in reductive coupling to provide products of propargylation 4 a4 l with good to complete levels of anti-diastereoselectivity. The unprotected tertiary hydroxy moiety of isopropoxy enyne 1 b is required to enforce diastereoselectivity. Deuterium-labeling studies corroborate reversible enyne hydrometalation in advance of carbonyl addition. As demonstrated in the conversion of 4 fh and 4 k to 5 fh and 5 k, the isopropoxy group of the product is readily cleaved upon exposure to aqueous sodium hydroxide to reveal the terminal alkyne.