Synthesis 2007(22): 3574-3588  
DOI: 10.1055/s-2007-990874
SPECIALTOPIC
© Georg Thieme Verlag Stuttgart · New York

Ruthenium-Catalyzed Transformations of Cyclopropylethynes [1]

Ingo Emmea, Christian Bruneaub, Pierre H. Dixneuf*b, Hans-Christian Militzera, Armin de Meijere*a
a Institut für Organische und Biomolekulare Chemie, Georg-August-Universität Göttingen, Tammannstraße 2, 37077 Göttingen, Germany
b Catalyse et Organométalliques UMR 6226, CNRS-Université de Rennes 1, Institut Sciences Chimiques de Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France
Fax: +49(551)399475; e-Mail: Armin.deMeijere@chemie.uni-goettingen.de;
Further Information

Publication History

Received 19 July 2007
Publication Date:
31 October 2007 (online)

Abstract

The addition of various carboxylic acids to (trans-2-ethoxycyclopropyl)ethyne (1) by catalysis with [Ru(O2CH)(CO)2(PPh3)]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(CH2CMeCH2)2(dppb)] catalysis to give 2-(trans-2-ethoxycyclopropyl)ethenyl esters 13 (69-92%, 3 examples). (1-Hydroxycyclopropyl)ethyn­e (14), under catalysis by [Ru(O2CH)(CO)2(PPh3)]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(CH2CMeCH2)2(dppb)] and [Ru(O2CH)(CO)2(PPh3)]2 to furnish 2-cyclopropylethenyl esters 23 (68-98%, 6 examples) and 1-cyclopropylethenyl esters 24 (66-97%, 5 examples), respectively.

12

The ring closure in this sequence9f is best performed with LiHMDS, not with LDA.9g Subsequent complete isomerization of the cis- to the trans-isomer in the initially obtained mixture is then achieved by treatment with LDA for 5 min.

25

It is noteworthy that the amount of catalyst is critical in this reaction. When less than 1 mol% of C was used, an increasing amount of the 1-substituted vinyl ester was observed. The prolonged reaction time allowed the catalyst to alter (be oxidized?) and obviously the altered species still catalyzes the addition but with diminished selectivity.