Solvent- and Ligand-free Diboration of Alkynes and Alkenes Catalyzed by Platinum Nanoparticles on Titania

Platinum nanoparticles supported on titania efficiently catalyzed the diboration of alkynes and alkenes under solvent- and ligand-free conditions in air. The cis-1,2-diborylalkenes and 1,2-diborylalkanes were obtained in moderate to excellent yields following, in most cases, a simple filtration workup protocol. The versatility of the cis-1,2-diboronvinyl compounds was demonstrated in a series of organic transformations, including the Suzuki–Miyaura cross coupling and the boron–halogen exchange.

Direct Nucleophilic Substitution of Free Allylic Alcohols in Water Catalyzed by FeCl3⋅6 H2O: Which is the Real Catalyst?

The allylic substitution reaction, and particularly the direct allylic amination reaction, of free allylic alcohols in water catalyzed by FeCl3⋅6 H2O is described. This novel environmentally-friendly methodology allows the use of a wide variety of nitrogenated nucleophiles such as sulfonamides, carbamates, benzamides, anilines, benzotriazoles, and azides, generally giving good yields of the corresponding substitution products. The synthetic applicability of the process is also demonstrated because the reaction can be performed on gram-scale. Additionally, carbon nucleophiles such as silylated nucleophiles, aromatic compounds, and malonates also proved to be suitable for this transformation. Finally, the nature of the catalytic species present in aqueous media is unveiled, pointing towards the formation of hexaaquo iron(III) complexes.

Enantioselective aldol reactions with aqueous 2,2-dimethoxyacetaldehyde organocatalyzed by binam-prolinamides under solvent-free conditions

Aqueous 2,2-dimethoxyacetaldehyde (60% wt solution) is used as an acceptor in aldol reactions, with cyclic and acyclic ketones and aldehydes as donors, organocatalyzed by 10 mol % of N-tosyl-(Sa)-binam-l-prolinamide [(Sa)-binam-sulfo-l-Pro] at rt under solvent-free conditions. The corresponding monoprotected 2-hydroxy-1,4-dicarbonyl compounds are obtained in good yields and with high levels of diastereo- and enantioselectivity mainly as anti-aldols. In the case of 4-substituted cyclohexanones a desymmetrization process takes place to mainly afford the anti,anti-aldols. 2,2-Dimethyl-1,3-dioxan-5-one allows the synthesis of a useful intermediate for the preparation of carbohydrates in higher yield, de and ee than with l-Pro as the organocatalyst.

1,2-Functionalized Imidazoles as Palladium Ligands: An Efficient and Robust Catalytic System for the Fluorine-Free Hiyama Reaction

A variety of hydroxy- and amino-functionalized imidazoles were prepared from 1-methyl- and 1-(diethoxymethyl)imidazole by means of isoprene-mediated lithiation followed by reaction with an electrophile. These compounds in combination with palladium acetate were screened as catalyst systems for the Hiyama reaction under fluorine-free conditions using microwave irradiation. The systematic study of the catalytic system showed 1-methyl-2-aminoalkylimidazole derivative L1 to be the best ligand, which was employed under solvent-free conditions with a 1:2 Pd/ligand ratio and TBAB (20 mol-%) as additive. The study has revealed an interaction between the Pd/ligand ratio and the amount of TBAB. The established catalytic system presented a certain degree of robustness, and it has been successfully employed in the coupling of a range of aryl bromides and chlorides with different aryl siloxanes. Furthermore, both reagents were employed in an equimolecular amount, without an excess of organosilane.

Bis(2-aminobenzoimidazole)-Organocatalyzed Asymmetric Alkylation of Activated Methylene Compounds with Benzylic and Allylic Alcohols

The first organocatalyzed asymmetric alkylation of activated methylene compounds using benzylic and allylic alcohols as alkylating agents through dual hydrogen bond activation in an SN1-type reaction is reported. This green protocol employs a bis(2-aminobenzoimidazole) in combination with an achiral Brønsted acid as a bifunctional catalytic system and gives the alkylation products with moderate to good enantioselectivities. Although the scope of the reaction is limited, this methodology can be considered as complementary to existing metal-catalyzed processes. In addition, modest results were obtained in a first attempt to perform a metal-free asymmetric Tsuji–Trost reaction using allylic alcohols. Finally, the recovery and reusability of the organocatalyst is also achieved.