Synthesis of 1-(alkoxycarbonyl)methylene-1,3-dihydroisobenzofurans and 4-alkoxycarbonylbenzo[c]pyrans by palladium-catalysed oxidative carbonylation of 2-alkynylbenzyl alcohols, 2-alkynyl benzaldehydes and 2-alkynylphenyl ketones

A direct synthesis of 1-(alkoxycarbonyl)methylene-1,3-dihydroisobenzofurans2 and 5 and 4-(alkoxycarbonyl)benzo[c]-pyrans 3 and 6 by oxidative Pd-catalysed cyclization/alkoxycarbonylationof 2-alkynylbenzyl alcohols 1, and of 2-alkynylbenzaldehydesor 2-alkynylphenyl ketones 4 is reported.Reactions were carried out in ROH or CH3CN/ROH (R = Me,iPr) as the solvent at 70−105 °C in the presence of catalyticamounts of PdI2 in conjunction with KI under a 4:1 or 3:1CO/air mixture (2.0 or 3.2 MPa total pressure at 25 °C). Thereaction occurs through intramolecular attack by the nucleo-IntroductionThe use of the catalytic system based on PdI2 in conjunctionwith an excess of KI in the oxidative carbonylation ofalk-1-ynes, disclosed by us some years ago,[1] has provedvery valuable for performing carbonylative cyclisation reactionsleading to the selective formation of important heterocyclicderivatives.[2] In particular, we have recently shownthat (Z)-2-en-4-yn-1-ols can be efficiently and selectivelyconverted into furan-2-ylacetic esters through an anti-5-exo-dig cyclisation process followed by alkoxycarbonylationand aromatisation.[2] We now wish to report a new synthesisof 1-(alkoxycarbonyl)methylene-1,3-dihydroisobenzofurans[a] Dipartimento di Chimica Generale ed Inorganica, ChimicaAnalitica, Chimica Fisica, Universita` di Parma,Parco Area delle Scienze 17A, 43100 Parma, Italy[b] Dipartimento di Chimica Organica e Industriale, Universita` diParma,Parco Area delle Scienze 17A, 43100 Parma, ItalyFax: (internat.) 39-0521/905-472E-mail: mirco.costa@unipr.it[c] Dipartimento di Chimica Universita` della Calabria,87036 Arcavacata di Rende, Cosenza, Italy[d] Dipartimento di Scienze Farmaceutiche, Universita` dellaCalabria,87036 Arcavacata di Rende, Cosenza, ItalyFax: (internat.) 39-0984/492-044E-mail: b.gabriele@unical.itSupporting information for this article is available on theWWW under http://www.eurjoc.org or from the author.574  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ejoc.200300577 Eur. J. Org. Chem. 2004, 574585philic oxygen atom (either already present in the startingmaterial, as in 1, or generated in situ by ROH attack on carbonylgroup, as in 4) on the triple bond coordinated to PdII,followed by alkoxycarbonylation. The presence of substituentsat the alkyne terminal position and at the carbon atomα to the hydroxy group play a key role in the selectivity ofthe process towards the formation of a five- or six-memberedring.