Anti-Selective Vicinal Silaboration and Diboration of Alkynoates through Phosphine Organocatalysis

Organocatalytic silyl transfer from silylborane to nitroalkenes for the synthesis of β-silyl nitroalkanes and β-silyl amines

We discovered organocatalytic silyl transfer from silylborane to nitroalkenes in a toluene/water biphasic solvent. A variety of functionalized β-silyl nitroalkanes were obtained in moderate to excellent yields, which provides access to biologically interesting β-silyl amines.

Synthesis of 1,1-Diborylalkenes through a Brønsted Base Catalyzed Reaction between Terminal Alkynes and Bis(pinacolato)diboron

A method for the synthesis of 1,1-diborylalkenes through a Brønsted base catalyzed reaction between terminal alkynes and bis(pinacolato)diboron has been developed. The procedure allows direct synthesis of functionalized 1,1-diborylalkenes from various terminal alkynes including propiolates, propiolamides, and 2-ethynylazoles.

Boron-selective reactions as powerful tools for modular synthesis of diverse complex molecules

In the context of modular and rapid construction of molecular diversity and complexity for applications in organic synthesis, biomedical and materials sciences, a generally useful strategy has emerged based on boron-selective chemical transformations. In the last decade, these types of reactions have evolved from proof-of-concept to some advanced applications in the efficient preparation of complex natural products and even automated precise manufacturing on the molecular level. These advances have shown the great potential of boron-selective reactions in simplifying synthetic design and experimental operations, and should inspire new developments in related chemical and technological areas. This tutorial review will highlight the original contributions and representative advances in this emerging field.

Mechanism of NHC-Catalyzed Conjugate Additions of Diboron and Borosilane Reagents to α,β-Unsaturated Carbonyl Compounds

Broadly applicable enantioselective C-B and C-Si bond-forming processes catalyzed by an N-heterocyclic carbene (NHC) were recently introduced; these boryl and silyl conjugate addition reactions (BCA and SCA, respectively), which proceed without the need for a transition-metal complex, represent reaction pathways that are distinct from those facilitated by transition-metal-containing species (e.g., Cu, Ni, Pt, Pd, or Rh based). The Lewis-base-catalyzed (NHC) transformations are valuable to chemical synthesis, as they can generate high enantioselectivities and possess unique chemoselectivity profiles. Here, the results of investigations that elucidate the principal features of the NHC-catalyzed BCA and SCA processes are detailed. Spectroscopic evidence is provided illustrating why the presence of excess base and MeOH or H2O is required for efficient and enantioselective boryl and silyl addition reactions. It is demonstrated that the proton sources influence the efficiency and/or enantioselectivity of NHC-catalyzed enantioselective transformations in several ways. The positive, and at times adverse, impact of water (biphasic conditions) on catalytic enantioselective silyl addition reactions is analyzed. It is shown that a proton source can facilitate nonenantioselective background reactions and NHC decomposition, requiring the catalyst to surpass such complications. Stereochemical models are presented that account for the identity of the observed major enantiomers, providing a rationale for the differences in selectivity profiles of BCA and SCA processes.

(E)- and (Z)-stereodefined enol phosphonates derived from β-ketoesters: stereocomplementary synthesis of fully-substituted α,β-unsaturated esters

A versatile, robust, and stereocomplementary synthesis of fully-substituted (E)- and (Z)-stereodefined α,β-unsaturated esters 3 from accessible α-substituted β-ketoesters 1via (E)- and (Z)-enol phosphonates was achieved.