Enantioselective Hydroalkenylation and Hydroalkynylation of Alkenes Enabled by a Transient Directing Group: Catalyst Generality through Rigidification.

The catalytic enantioselective synthesis of α-chiral alkenes and alkynes represents a powerful strategy for rapid generation of molecular complexity. Herein, we report a transient directing group (TDG) strategy to facilitate site-selective palladium-catalyzed reductive Heck-type hydroalkenylation and hydroalkynylation of alkenylaldehyes using alkenyl and alkynyl bromides, respectively, allowing for construction of a stereocenter at the δ-position with respect to the aldehyde. Computational studies reveal the dual beneficial roles of rigid TDGs, such as L-tert-leucine, in promoting TDG binding and inducing high levels of enantioselectivity in alkene insertion with a variety of migrating groups.

Construction of congested Csp3-Csp3 bonds by a formal Ni-catalyzed alkylboration.

Through the combination of a Ni-catalyzed alkene alkenylboration followed by hydrogenation, the synthesis of congested Csp3-Csp3-bonds can be achieved. Conditions have been identified that allow for the use of both alkenyl-bromides and -triflates. In addition, the hydrogenation creates another opportunity for stereocontrol, thus allowing access to multiple stereoisomers of the product. Finally, the method is demonstrated in the streamlined synthesis of a biologically relevant molecule.

Allenylidene Induced 1,2-Metalate Rearrangement of Indole-Boronates: Diastereoselective Access to Highly Substituted Indolines.

A process to achieve 1,2-metalate rearrangements of indole boronate as a way to access substituted indolines in high diastereoselectivities is presented. The reaction involves the generation of a Cu-allenylidene, which is sufficiently electrophilic to induce the 1,2-metalate rearrangement. The scope of the reaction is evaluated as well as further transformations of the product.

Catalytic Arylboration of Spirocyclic Cyclobutenes: Rapid Access to Highly Substituted Spiro[3.n]alkanes.

A method to achieve the synthesis of highly substituted spirocyclic cyclobutanes is disclosed. The reaction involves the catalytic arylboration of cyclobutenes. Depending on the substitution pattern of the cyclobutene, either a Cu/Pd- or a Ni-catalyzed reaction was utilized. In the case of the Cu/Pd catalyzed reactions, the identification of a Cu-complex for arylboration was crucial to observe high selectivity. The synthetic utility of the products is demonstrated, and the mechanistic details are discussed.

Enantioselective [4 + 2]-Annulation of Azlactones with Copper-Allenylidenes under Cooperative Catalysis: Synthesis of α-Quaternary α-Acylaminoamides.

The first enantioselective decarboxylative [4 + 2]-annulation of ethynyl benzoxazinanones with azlactones has been developed under cooperative copper and bifunctional tertiary aminourea catalysis. This direct and modular approach combines dipolar copper-allenylidene intermediates with azlactone enolates and allows for the synthesis of α-quaternary α-acylaminoamides as a single diastereomer generally in high yields with good to excellent enantioselectivities (up to 99:1 er).

A Catalytic Enantioselective Iodocyclization Route to Dihydrooxazines.

The first catalytic enantioselective synthesis of 5,6-dihydro-4H-1,2-oxazines bearing an oxygen-containing quaternary stereogenic center has been developed through iodoetherification of γ,δ-unsaturated oximes. This operationally straightforward reaction is catalyzed by Cinchona alkaloids-based bifunctional tertiary aminothiourea derivatives and furnishes the products generally in good to excellent yields and with moderate to high enantioselectivities (up to 97:3 er).

Catalytic Enantioselective Synthesis of 3,4-Unsubstituted Thiochromenes through Sulfa-Michael/Julia-Kocienski Olefination Cascade Reaction.

A highly enantioselective cascade sulfa-Michael/Julia-Kocienski olefination reaction between 2-mercaptobenzaldehydes and ß-substituted vinyl PT-sulfones has been realized for the synthesis of 3,4-unsubstituted 2H-thiochromenes. This reaction, catalyzed by diphenylprolinol TMS ether, proceeds through an aromatic iminium intermediate and furnishes a wide range of 2-substiuted 2H-thiochromenes with excellent enantioselectivities (up to 99:1 er).