Ruthenium-Catalyzed Transformations of Cyclopropylethynes

Abstract The addition of various carboxylic acids to (TRANS-2-ethoxycyclopropyl)ethyne (1) by catalysis with [Ru(O 2 CH)(CO) 2 (PPh 3 )] 2 proceeds regioselectively in the Mar­kovnikov sense with ring opening of the cyclopropyl group to furnish allenylacetaldehyde acyl ethyl acetals 3 in high yields (44-96%, 11 examples). The allenylacetaldehyde derivatives undergo palladium-catalyzed Heck-type cross coupling with iodobenzene and subsequent trapping of the π-allylpalladium intermediate with primary and secondary amines to yield labile [β-(1-aminomethyl)styryl]acetaldehyde acyl ethyl acetals 12 (24-83%, 4 examples). Anti-Markovnikov addition of carboxylic acids to the triple bond in (TRANS-2-ethoxycyclopropyl)ethyne (1) without ring opening can be brought about under [Ru(CH 2 CMeCH 2 ) 2 (dppb)] catalysis to give 2-(TRANS-2-ethoxycyclopropyl)ethenyl esters 13 (69-92%, 3 examples). (1-Hydroxycyclopropyl)ethyn­e (14), under catalysis by [Ru(O 2 CH)(CO) 2 (PPh 3 )] 2 , reacts with carboxylic acids to yield 1-acetylcyclopropyl esters 15 (49-74%, 4 examples) by Markov­nikov-sense addition and intramolecular transesterification. Anti-Markovnikov- and Markovnikov-sense addition of carboxylic acids to unsubstituted cyclopropylethyne can both be achieved regioselectively under catalysis with [Ru(CH 2 CMeCH 2 ) 2 (dppb)] and [Ru(O 2 CH)(CO) 2 (PPh 3 )] 2 to furnish 2-cyclopropylethenyl esters 23 (68-98%, 6 examples) and 1-cyclopropylethenyl esters 24 (66-97%, 5 examples), respectively.