Trifluoroacetic anhydride—catalyzed conjugate addition of boronic acids to α,β-unsaturated ketones

Crown Ether-Derived Chiral BINOL: Enantioselective Michael Addition of Alkenyl Boronic Acids to α,β-Unsaturated Ketones

A new class of aza-crown ether-derived chiral BINOL catalysts were designed, synthesized, and applied in the asymmetric Michael addition of alkenylboronic acids to α,β-unsaturated ketones. It was found that introducing aza-crown ethers to the BINOL catalyst could achieve apparently higher enantioselectivity than a similar BINOL catalyst without aza-crown ethers did, although the host-guest complexation of alkali ions by the aza-crown ethers could not further improve the catalysis effectiveness. Under mediation of the aza-crown ether-derived chiral BINOL and in the presence of a magnesium salt, an array of chiral γ,δ-unsaturated ketones were furnished in good enantioselectivities (81-95% ees).

Nucleophilic halo-Michael addition under Lewis-base activation

A simple and general conjugate nucleophilic halogenation is presented. The THTO/halosilane combination has shown the ability to act as a nucleophilic halide source in the conjugate addition to a variety of Michael acceptors. In addition, a straightforward diastereoselective halogen installation using α,β-unsaturated acyloxazolidinones as platforms has been developed.

Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism

The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism-nucleophilic attack of enolate oxygen on Palladium followed by C-C bond-forming [3,3']-reductive elimination.

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.