Palladium-catalysed alkylative cyclisation of 2,3-butadienylmalonates to γ-lactones

Palladium-catalysed inter- and intramolecular formation of C–O bonds from allenes

This review highlights the Pd-catalysed formation of a C–O bond from allenes via the inter- or intramolecular reaction.

PdII-Catalyzed Oxidative Dimeric Cyclization-Coupling Reaction of 2,3-Allenoic Acids: An Efficient Synthesis of Bibutenolide Derivatives

Three sets of convenient catalytic systems have been developed for the oxidative dimeric cyclization coupling of differently substituted 2,3-allenoic acids catalyzed by Pd(II), affording bibutenolides that are not otherwise readily available. The advantages and disadvantages of these systems are discussed. Although the diastereoselectivity for the bicyclization of racemic 2,3-allenoic acids is low, excellent diastereoselectivity was realized in the bicyclization reaction of optically active 2,3-allenoic acids, leading to the optically active bibutenolides in high yields and ee. Based on a mechanistic study, it is believed that the reaction may proceed by means of a double oxypalladation and reductive elimination to yield butenolide 3 and Pd(0) species, which may be reoxidized to the catalytically active Pd(II) species in the presence of alkyl iodide/air, metallic iodide/air, or benzoquinone.

Highly Regio- and Stereoselective Synthesis of Polysubstituted Cyclopropane Compounds via the Pd(0)-Catalyzed Coupling−Cyclization Reaction of 2-(2‘,3‘-Allenyl)malonates with Organic Halides

A new method for highly regio- and stereoselective synthesis of polysubstituted cyclopropane compounds via the Pd(0)-catalyzed coupling-cyclization reaction of 2-(2',3'-allenyl)malonates with organic halides is described. In these reactions, the starting materials are easily available and the operation is convenient. The ratios of trans-isomer/cis-vinylic cyclopropanes are up to 98:2.

Control of regioselectivity in Pd(0)-catalyzed coupling-cyclization reaction of 2-(2',3'-allenyl)malonates with organic halides

The regioselectivity in the Pd(0)-catalyzed coupling-cyclization of 2-(2',3'-allenyl)malonates with organic halides is determined by the steric and electronic effects of both substrates. By deliberate control of the reaction conditions, the regioselectivity of this reaction can be tuned. With conditions A and B, the reaction afforded vinylic cyclopropane derivatives, while with conditions C and D, the reaction afforded cyclopentene derivatives in a highly selective manner. Under similar conditions, 1-alkenyl halides tend to form more three-membered cyclic products. The increased steric hindrance at the 2'-position of the allene moiety and aryl halides favors the formation of five-membered cyclic products. The regioselectivity of the reaction may be explained by the comparison of the relative stabilities of syn- and anti-type pi-allyl palladium intermediates.

Reverse of regioselectivity in intramolecular nucleophilic substitution of pi-allyl palladium species. Highly selective formation of vinylic cyclopropanes via the Pd(0)-catalyzed coupling-cyclization reaction of organic iodides with 2-(2', 3'-Dienyl)malonates

Vinylic cyclopropanes were formed highly selectively via the Pd(PPh(3))(4)-catalyzed insertion-intramolecular nucleophilic substitution reaction of aryl or 1-alkenyl iodides with 2-(2', 3'-dienyl)malonates. The regioselectivity observed here is different from what was reported by Cazes et al.