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. Author manuscript; available in PMC: 2010 Nov 11.
Published in final edited form as: J Am Chem Soc. 2009 Nov 11;131(44):16054–16062. doi: 10.1021/ja906225n

Scheme 3.

Scheme 3

Rhodium catalyzed coupling of acetylene to aldehyde 14a in the absence of hydrogen and Brønsted acid cocatalyst delivers ketone 14b, corroborating intervention of the proposed oxarhodacycloheptadiene intermediate.