Pd-Catalyzed Three-Component Reaction of 3-(Pinacolatoboryl)ally Acetates, Aldehydes, and Organoboranes: A New Entry to Stereoselective Synthesis of (Z)-anti-Homoallylic Alcohols

Copper-Catalyzed Diastereo-, Enantio-, and (Z)-Selective Aminoallylation of Ketones through Reductive Couplings of Azatrienes for the Synthesis of Allylic 1,2-Amino Tertiary Alcohols

We introduce a method for the (Z)-selective aminoallylation of a range of ketones to prepare allylic 1,2-amino tertiary alcohols with excellent diastereo- and enantioselectivity. Copper-catalyzed reductive couplings of 2-azatrienes with aryl/alkyl and dialkyl ketones proceed with Ph-BPE as the supporting ligand, generating anti-amino alcohols with >98% (Z)-selectivity under mild conditions. The utility of the products is highlighted through several transformations, including those that leverage the (Z)-allylic amine moiety for diastereoselective reactions of the alkene. Calculations illustrate Curtin-Hammett control in the product formation over other possible isomers and the origin of (Z)-selectivity.

Access to a pair of ambiphilic phosphine-borane regioisomers by rhodium-catalyzed hydroboration

Lewis basic substrates, such as vinylphosphines and enamines, can be problematic for transition-metal catalysed hydrofunctionalization reactions due to their propensity to ligate and deactivate transition-metal catalysts as well as form direct Lewis adducts with reaction partners. While exploring rhodium-catalyzed hydroboration of diphenylvinylphosphine with pinacolborane, we found that a high degree of regiocontrol could be achieved without the need to diminish the Lewis basicity of the phosphine by oxidation or prior-protection. At slightly elevated temperature, a high yield of the previously unreported branched regioisomer, 1-pinacolatoborono-1-diphenylphosphinoethane, was achieved with regioselectivity greater than 10 : 1 using [Rh(COD)Cl]2 as the catalyst and AgOTf as a catalytic additive. Inversion of regioselectivity occurred at low temperature and high yield of the linear regioisomer was observed. Subsequent functionalization of the new branched phosphine-boronic ester and its coordination to rhodium were also investigated.

A Simple Procedure for the Synthesis of β-Hydroxyallenamides via Homoallenylation of Aldehydes

A simple one-pot synthesis of β-hydroxyallenamides is reported. This procedure entails chemo- and regioselective hydroboration of 3-en-1-ynyl-sulfonylamides with Cy₂BH followed by homoallenylation of aldehydes to yield β-hydroxyallenamides (up to 94% yield and >20:1 dr). Controlled synthesis of up to three continuous stereochemical elements was realized. Density functional theory (DFT) calculations suggest a concerted Zimmerman-Traxler chair-like transition state. Initial results suggest that enantio- and diastereoselective synthesis of β-hydroxyallenamides with optically active hydroboration reagents is viable.

Transition-Metal-Free Borylation of Allylic and Propargylic Alcohols

The base-catalyzed allylic borylation of tertiary allylic alcohols allows the synthesis of 1,1-disubstituted allyl boronates, in moderate to high yield. The unexpected tandem performance of the Lewis acid-base adduct, [Hbase](+) [MeO-B2 pin2 ](-) favored the formation of 1,2,3-triborylated species from the tertiary allylic alcohols and 1-propargylic cyclohexanol at 90 °C.

Single-Flask Multicomponent Palladium-Catalyzed α,γ-Coupling of Ketone Enolates: Facile Preparation of Complex Carbon Scaffolds

A three-component palladium-catalyzed reaction sequence has been developed in which γ-substituted α,β-unsaturated products are obtained in a single flask by an α-alkenylation with either a subsequent γ-alkenylation or γ-arylation of a ketone enolate. Coupling of a variety of electronically and structurally different components was achieved in the presence of a Pd/Q-Phos catalyst (2 mol %), usually at 22 °C with yields of up to 85 %. Most importantly, access to these products is obtained in one simple operation in place of employing multiple reactions.