An environmentally benign Au(III)-catalyzed regio- and stereoselective domino synthesis of oxazolo fused pyridoindoles 7a-v and benzofurooxazolo pyridines 8a-n by the reaction of o-alkynylaldehydes 4a-t and 5a-k with (S)-phenylglycinol 6a and (R)-phenylglycinol 6b under mild reaction conditions using water as reaction medium is reported. The reaction proceeded via selective C-N bond formation on the more electrophilic alkynyl carbon through 6-endo-dig cyclization. The reaction tolerates a wide variety of functional groups. The developed chemistry has been successfully extended for the synthesis of a diverse class of γ-carbolines and benzofuro[3,2-c]pyridines using corresponding ester hydrochlorides of serine, threonine, and cystine as a nitrogen source.

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An operationally simple silver-catalyzed tandem strategy for the synthesis of benzothienopyridines 7a-t and benzofuropyridines 8a-p by the reaction of o-alkynyl aldehyde 4a-t and 5a-p with tert-butylamine 6 under mild reaction conditions is described. The present methodology provides a facile conversion of easily accessible o-alkynyl aldehydes into medicinally useful heterocycles in good to excellent yields under mild and environmentally friendly reaction conditions with excellent regioselectivity. The developed chemistry has been successfully extended for the selective synthesis of C-4 deuterated benzothienopyridines 7u-v and benzofuropyridines 8q-r. The role of the ethanolic proton in the reaction was validated by deuterium-labeling experiments.

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