Catalytic Asymmetric Synthesis of Chiral Propargylic Boron Compounds through B–H Bond Insertion Reactions

Abstract

Chiral propargylic boron compounds have a diverse array of potential applications. Although numbers of highly enantioselective methodologies for the synthesis of other organoboron compounds are well established, highly enantioselective synthesis of chiral propargylic boron compounds remains unknown. Herein, we report a catalytic method for the construction of chiral propargylic boron compounds by means of highly enantioselective dirhodium-catalyzed B−H bond insertion reactions using aryl propargylic sulfonylhydrazones as carbene precursors. This method enables the straightforward synthesis of a wide range of stable chiral propargylic boron compounds in yields up to 99% with enantioselectivities up to 97% ee. The operationally simple method features a broad substrate scope, good functional group tolerance, and mild reaction conditions. The boron compounds prepared in this study are inaccessible by other known methods and exhibit high potential utility because they could be efficiently transformed into allenyl borates, triazole borane compounds, and homopropargylic and propargylic alcohols with good enantiomeric fidelity. Our work expands the library of catalytic B−H bond insertion reactions, increases the variety of chiral organoboron compounds that can be synthesized, and provides preliminary information about possible transformations of chiral propargylic boron compounds, thus laying the foundation for wide application of these compounds.

Synthesis of Alkynyl Hydrazones from Unprotected Hydrazine and Their Reactivity as Diazo Precursors

“…9 To the best of our knowledge, the reactivity of functionalized diazo species A is merely limited to a cyclopropanation and a multi-component reaction via Rh catalysis, 7,11,12 whereas hydrazone B was utilized for a Si−H bond insertion reaction via Rh catalysis. 13 Noticeably, alkynyl N-sulfonyl hydrazones C have emerged as the desirable alkynyl carbene precursors because they could successfully be employed for cyclopropanation 14 and Si−H, 15 B−H, 16 and C−C bond 17 insertion reactions via Rh/Ag catalysis. In this regard, the precursors C were carefully designed by tailoring sterically bulky Ns/Tris groups on the aryl sulfonyl group of hydrazones (Scheme 1b).…”

Rh-Catalyzed [2,3]-Sigmatropic Rearrangement of Alkynyl Carbenes with Allyl Sulfides to Access Sulfide-Substituted 1,5-Enynes

“…The readiness and operational safety of alkynyl N -tosylhydrazones make them an ideal and valuable alkynylcarbene precursor. − However, easy intramolecular cyclization to generate pyrazoles , limits the use of this precursor. Bi and Zhu’s groups employed N -nosylhydrazone and N -trisylhydrazone, respectively, − and solved the problem through a related carbene-transfer reaction (Figure A). − Inspired by those results and our continued interest in the N -sulfonylhydrazones chemistry, − we here report an Rh-catalyzed [2,3]-sigmatropic rearrangement of alkynyl carbenes with allyl sulfides that yields sulfides substituted 1,5-enyne products, which have been recognized as highly versatile substrates for the construction of cyclic structures . To the best of our knowledge, this transformation represents the first [2,3]-sigmatropic rearrangement of alkynyl carbenes.…”

Recent advances in the construction of tetracoordinate boron compounds

“…And the asymmetric version 12 b of aryl diazo compounds was reported by Zhu and Zhou. In 2022, Zhu's group 13 replaced the aryl group with an ethynyl propylene group in diazo compounds and realized the B–H bond insertion of tetracoordinate boranes under rhodium catalysis to obtain ethynyl boron products 7 . Wang's group disclosed the synthesis of 8 via a copper catalyzed B–H bond insertion of 4-diazo-1,4-dihydroisoquinolin-3-ones with an amine–borane adduct in 2021.…”