Trifluoroacetic Anhydride Promoted Tandem Conjugate Addition of Boronic Acids/Acetal Ring Opening

Efficient conversion of d-mannitol into 1,2:5,6-diacetonide with Aquivion-H as a recyclable catalyst

Heterogeneous solid catalysis by the commercially available perfluorosulfonic ionomer Aquivion-H allowed 1,2:5,6-diacetonide of d-mannitol (1), immediate precursor of important unichiral C3-synthons, to be efficiently obtained from d-mannitol and 2,2-dimethoxypropane in DMF at room temperature. The 1,2-monoacetonide, whose intermediate formation is the rate-limiting step, could be almost completely converted into 1 with limited concurrent transformation of 1 into triacetonides. In line with recent literature reports, these results indicate that heterogeneous catalysis by Aquivion-H surpasses the performances of homogeneous acidic catalysis assuring, presumably for its peculiar morphology, a higher product selectivity. Easy recovery at the end of the reaction and recyclability are additional advantages of this solid acid catalyst.

Selective Functionalization of Achmatowicz Rearrangement Products by Reactions with Potassium Organotrifluoroborates under Transition-Metal-Free Conditions

The repertoire of synthetic transformations of the products of the Achmatowicz rearrangement has been expanded by exploring their reactivity with potassium organotrifluoroborates in the absence of transition metals. Depending on the reaction conditions and the substitution pattern of the starting material, the reaction may lead to the stereoselective synthesis of dihydropyranones (2,6- trans), tetrahydropyranones (2,3- cis-2,6- cis) or functionalized 1,4-dicarbonyl compounds. The method has also been adapted for the one-pot synthesis of functionalized pyrroles.

O-Monoacyltartaric acid catalyzed enantioselective conjugate addition of a boronic acid to dienones: application to the synthesis of optically active cyclopentenones

Enantioselective conjugate addition of styrylboronic acid to dienones was effectively catalyzed by an O-monoacyltartaric acid to afford monostyrylated products with good enantioselectivity. The RCM of the monostyrylated products using the Hoveyda-Grubbs II catalyst afforded optically active cyclopentenones, including a synthetic intermediate of the antitumor agent TEI-9826. The study shows that a diene additive such as 1,6-heptadiene or diallyl ether was essential for the RCM.

A hydrogen bond rationale for the enantioselective β-alkenylboration of enones catalyzed by O-monoacyltartaric acids

DFT calculations suggest that O-monoacyl L-tartaric acids catalyze the asymmetric conjugate alkenylboration of enones through transition structures that are stabilized by hydrogen-bonding interactions. Formation of a five-membered acyloxyborane is proposed. The hydrogen of the free carboxy group derived from the catalyst interacts with the carbonyl group of the cyclic acyloxyborane, stabilizing the transition structure and reducing the flexibility of the system. Additional stabilizing nonclassical CH···O hydrogen-bond interactions seem to determine the observed enantioselectivity.

Diels–Alder reactions of pinacol alkenylboronates: an experimental and theoretical study

We have studied the Diels–Alder reactions of pinacol alkenylboronates with cyclopentadiene under two different sets of conditions: thermal heating at 170 °C in a pressure tube and with catalytic TFA (5 mol%) at 80 °C.

Transition-metal-free C–C bond forming reactions of aryl, alkenyl and alkynylboronic acids and their derivatives

Transition-metal-free C–C bond forming reactions of boronic acids are new emerging tools in organic synthesis which complement metal-based procedures.