Palladium-Catalyzed Alkoxycarbonylation of (Z)-2-En-4-yn Carbonates Leading to 2,3,5-Trienoates

Abstract

Pd(0)-catalyzed carbonylation of (Z)-2-en-4-yn carbonates in the presence of a balloon pressure of CO in an alcohol donates vinylallenyl esters with an exclusively E-configuration and in high yields. The fact that no such reactivity could be observed with E-configured enyne carbonates may indicate that the reaction is promoted via the cooperative coordination of palladium with both alkynyl and carbonate moieties. Supporting Information Available. Detailed experimental procedures, and compound characterization data. This material is available free of charge via the Internet at http://pubs.acs.org.

Regio- and Stereoselective Synthesis of 2,3,5-Trienoates by Palladium-Catalyzed Alkoxycarbonylation of Conjugated Enyne Carbonates

“…11 This lower tolerance of the method on larger substituents on (Z)-isomers may be related to their overall more sterically congested structure as compared to their (E)-configured counterparts.…”

“…28 The mixture of S6j and its regioisomer (Z)-ethyl 2-(2,2-dimethylpropylidene)oct-3-ynoate was reduced to the corresponding primary enyne alcohols as specified previously. 11,12 The enyne alcohol of desired isomeric form S2j could be separated from its regioisomer by silica gel column chromatrography (hexane/ethyl acetate, yield: 1.8 g, 48%). S2j was oxidized to yield the corresponding enyne aldehyde S7j in 77% (1.4 g), and S7j was then subjected to Grignard reaction with MeMgBr following the procedures as described previously.…”

“…11,12 In that report, we have concluded that only (Z)-isomers of the enyne carbonate substrates were capable of taking part in this carbonylation reaction because the methoxycarbonylation of the substrate (E)-1a under the conditions established therein led to a complex mixture and consequently gave a low yield of the expected product 2aa (Scheme 2). 11 Repetitive trials by different hands has also resulted in similar failures.…”

“…We have found upon further study that, as reported herein, (E)-enyne carbonates are also applicable substrates. 11 Moreover, a good to excellent level of center-to-axial chirality transfer would be possible upon modification of the reaction conditions. In addition, observed stereoselectivity of the process, as well as structural features of various byproducts identified during several reactions, provided more information for the mechanism underlying the method.…”

A DFT study on the mechanism of palladium-catalyzed divergent reactions of 1,6-enyne carbonates

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21] The reactions of allenyl palladium with olefins as nucleophiles are well-known to form carbon−carbon bonds. [22][23][24][25] However, as most of these reactions produce corresponding allenic systems and subsequent rearranged derivatives, much less research interest has been paid to the propargylic substitution reactions of propargylic carbonates with olefins in Pd-catalyzed processes. 26-28 * For correspondence Recently, Liang et al 29 studied palladium-catalyzed divergent reactions of enyne carbonates by experiments to synthetise six-or five-membered compounds (scheme 1).…”