The unexpected and the unpredictable in organic synthesis

Organocatalytic Asymmetric α-Allylation and Propargylation of α-Branched Aldehydes with Alkyl Halides

Enantioselective α-allylation and -propargylation of α-branched aldehydes with alkyl halides was successfully performed using a chiral primary amino acid organocatalyst. This alkylation reaction, involving the generation of a chiral quaternary carbon stereocenter, proceeded smoothly in a mildly basic aqueous solution of potassium hydrogen carbonate to furnish α-allylated or -propargylated aldehydes in a good yield (up to 87%) and high enantioselectivity (up to 96% ee).

Achievements of the Late Professor Teruaki Mukaiyama

This essay illuminates the quintessence of the life of the late Professor Teruaki Mukaiyama, the founding editor of The Chemical Record. It shares first-hand knowledge of his heartfelt and enlightening mentorship as well as his major scientific contributions to the chemical community. It will serve as an ever-lasting message of the didactic guidance and encouragement he provided for the future generations.

Enantioselective hydrosilylation of unsaturated carbon-heteroatom bonds (C[double bond, length as m-dash]N, C[double bond, length as m-dash]O) catalyzed by [Ru-S] complexes: a theoretical study

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst [Ru–S] ([L*-Ru(SDmp)]⁺[BAr₄^F]⁻) with a chiral monodentate phosphine ligand is carried out in this work. We elucidate all the pathways leading to the main products or by products mediated by the [Ru–S] complex in order to have deep understanding of the chemoselectivity and enantioselectivity. The DFT (Density Functional Theory) calculations show that the reaction mechanism including: (1) Si–H bond cleavage by the dual activity of Ru–S bond; (2) the generation of a sulfur-stabilized silane cation; (3) the electrophilic attack of silane cation to NC/OC; (4) hydrogen transfer from Ru to carbon cation. The hydrosilylation products are found to be the final products rather than the dehydrogenative ones, which is consistent with the experimental results. The dehydrogenative silylation reaction pathways which give N- or O-silylated enamine/enol ether are reversible according to our calculations. The computational results also show that the electrophilic attack of silicon to NC/OC is the rate-determining step and the ee value can be improved significantly with more bulky model phosphine ligand based on the same calculation methods.

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst with a chiral monodentate phosphine ligand is carried out in this work.

One-pot bienzymatic cascade combining decarboxylative aldol reaction and kinetic resolution to synthesize chiral β-hydroxy ketone derivatives

A bienzymatic one-pot cascade was constructed for the synthesis of chiral β-hydroxy ketones with up to 99% ee and theoretical yields.

Polymer-supported PPh3 as a reusable organocatalyst for the Mukaiyama aldol and Mannich reaction

Polystyrene-supported PPh₃ (PS-PPh₃) catalyzes the aldol reaction of aldehydes and imines to give the corresponding products in good to high yields.

Asymmetric aldol reactions catalyzed by efficient and recyclable silica-supported proline-based peptides

A series of silica-supported proline-based peptides were synthesized and applied as catalysts for direct asymmetric intermolecular aldol reactions. Among these, a peptide with two L-proline units was found to be the most efficient one for the asymmetric aldol reactions between acetone and aromatic aldehydes. The reactions generated the corresponding products with satisfactory isolated yields (up to 97%) and enantiomeric excesses (up to 96%) in the presence of this catalyst (5 mol %). Furthermore, the silica-supported organocatalyst could be recovered and recycled by a simple filtration of the reaction solution and used for five consecutive trials without loss of its reactivity.

Stereoselective aldol additions of achiral ethyl ketone-derived trichlorosilyl enolates

Methods for the preparation of geometrically defined enoxy(trichlorosilanes) derived from ethyl ketone enolates have been developed. The addition of enoxy(trichlorosilanes) (trichlorosilyl enolates) to aldehydes proceeds with good yields in the presence of catalytic amounts of chiral phosphoramides. The reaction of Z-trichlorosilyl enolates to aryl aldehydes affords aldol products with good to excellent diastereo- and enantioselectivities. Phosphoramide-catalyzed aldol additions lacked substrate generality providing modest selectivities with unsaturated and aliphatic aldehydes. In all cases, the phosphoramide-catalyzed aldol addition of E-trichlorosilyl enolates to aldehydes provided good yields with moderate to good stereoselectivities.

The aldol addition reaction: an old transformation at constant rebirth

The main recent conceptual advances in asymmetric aldol reactions are presented. Methods ranging from stoichiometric chiral auxiliary-mediated to direct, catalytic reactions are covered, including the Mukaiyama aldol reactions which use stoichiometric base and silylating reagents, but catalytic (substoichiometric) amounts of the chiral inductor. The salient features of each new development are noted, paying special attention to practical concerns and to the potential implementation for large scale production. After examination of pros and cons of each strategy, gaps and limitations that deserve further investigation are highlighted.