Kalicharan Chattopadhyay

Decarboxylative Benzylations of Alkynes and Ketones

Benzyl esters of propiolic and beta-keto acids undergo catalytic decarboxylative coupling when treated with appropriate palladium catalysts. Such decarboxylative couplings allow the benzylation of alkynes without the use of strong bases and/or organometallics. This allows the synthesis of sensitive benzylic alkynes that are prone to undergo isomerizations under basic conditions. Additionally, decarboxylation facilitates the site-specific benzylation of diketones and ketoesters under mild, base-free conditions. Ultimately, the methodology described expands our ability to cross-couple medicinally relevant heterocycles.

Metal nanoparticles as efficient catalysts for organic reactions

Pd(0) nanoparticles have been demonstrated to be very efficient catalysts for C–C bond-forming reactions. These include coupling of vicinal-diiodoalkenes and acrylic esters and nitriles leading to the stereoselective synthesis of 2-alkene-4-yn-esters and nitriles, allylation of active methylene compounds by allyl acetate, and Hiyama cross-coupling of aryliodides with arylsilanes. Cu(0) nanoparticles catalyze aryl-sulfur bond formation, accomplishing the synthesis of functionalized aryl sulfides and aryl- and vinyl dithiocarbamates. Cu nanoparticles have also been used for the chemoselective reduction of aromatic nitro compounds.

Mechanistic Origin of the Stereodivergence in Decarboxylative Allylation

A stereochemical test has been used to probe the mechanism of decarboxylative allylation. This probe suggests that the mechanism of DcA reactions can change based on the substitution pattern at the alpha-carbon of the nucleophile; however, reaction via stabilized malonate nucleophiles is the lower energy pathway. Lastly, this mechanistic proposal has predictive power and can be used to explain chemoselectivities in decarboxylative reactions that were previously confounding.

Amphiphilic allylation of activated alkenes by allyl acetates and allylstannanes catalyzed by palladium nanoparticles: an easy access to stereodefined substituted cyclohexene derivatives

An efficient vicinal double allylation of activated alkenes by allyl acetates and allylstannanes catalyzed by palladium nanoparticles, generated in situ from palladium(II) chloride, has been demonstrated. Several activated alkenes produce functionalized 1,7-octadiene derivatives in one pot. The additions of substituted allyl acetates are highly regioselective. The Grubbs cyclization of octadiene derivatives gives an easy access to stereodefined substituted cyclohexene derivatives.

Potential of metal nanoparticles in organic reactions

Palladium(0) nanoparticle has been used as efficient catalyst for (a) the stereoselective synthesis of (E)- and (Z)-2-alkene-4-ynoates and —nitriles by a simple reaction of vic-diiodo-(E)-alkenes with acrylic esters and nitriles and (b) for the allylation of active methylene compounds by allylacetate and its derivatives. Copper(0) nanoparticle catalyzes aryl-sulfur bond formation very efficiently. All these reactions are ligand-free.