TY - JOUR
T1 - Generation and Application of Homoallylic α,α-Diboryl Radicals via Diboron-Promoted Ring-Opening of Vinyl Cyclopropanes
T2 - cis-Diastereoselective Borylative Cycloaddition**
AU - Vyas, Het
AU - Gangani, Ashvin J.
AU - Mini, Aiswarya
AU - Lin, Shengjia
AU - Chu, Jia Min
AU - Agee, Caitlyn O.
AU - Gabriel, Justin
AU - Williamson, R. Thomas
AU - Zhang, Yong
AU - Sharma, Abhishek
N1 - Publisher Copyright:
© 2023 Wiley-VCH GmbH.
PY - 2024/1/8
Y1 - 2024/1/8
N2 - Carbon-centered radicals stabilized by adjacent boron atoms are underexplored reaction intermediates in organic synthesis. This study reports the development of vinyl cyclopropyl diborons (VCPDBs) as a versatile source of previously unknown homoallylic α,α-diboryl radicals via thiyl radical catalyzed diboron-directed ring opening. These diboryl stabilized radicals underwent smooth [3+2] cycloaddition with a variety of olefins to provide diboryl cyclopentanes in good to excellent diastereoselectivity. In contrast to the trans-diastereoselectivity observed with most of the dicarbonyl activated VCPs, the cycloaddition of VCPDBs showed a remarkable preference for formation of cis-cyclopentane diastereomer which was confirmed by quantitative NOE and 2D NOESY studies. The cis-stereochemistry of cyclopentane products enabled a concise intramolecular Heck reaction approach to rare tricyclic cyclopentanoid framework containing the diboron group. The mild reaction conditions also allowed a one-pot VCP ring-opening, cycloaddition-oxidation sequence to afford disubstituted cyclopentanones. Control experiments and DFT analysis of reaction mechanism support a radical mediated pathway and provide a rationale for the observed diastereoselectivity. To the authors’ knowledge, these are the first examples of the use of geminal diboryl group as an activator of VCP ring opening and cycloaddition reaction of α-boryl radicals.
AB - Carbon-centered radicals stabilized by adjacent boron atoms are underexplored reaction intermediates in organic synthesis. This study reports the development of vinyl cyclopropyl diborons (VCPDBs) as a versatile source of previously unknown homoallylic α,α-diboryl radicals via thiyl radical catalyzed diboron-directed ring opening. These diboryl stabilized radicals underwent smooth [3+2] cycloaddition with a variety of olefins to provide diboryl cyclopentanes in good to excellent diastereoselectivity. In contrast to the trans-diastereoselectivity observed with most of the dicarbonyl activated VCPs, the cycloaddition of VCPDBs showed a remarkable preference for formation of cis-cyclopentane diastereomer which was confirmed by quantitative NOE and 2D NOESY studies. The cis-stereochemistry of cyclopentane products enabled a concise intramolecular Heck reaction approach to rare tricyclic cyclopentanoid framework containing the diboron group. The mild reaction conditions also allowed a one-pot VCP ring-opening, cycloaddition-oxidation sequence to afford disubstituted cyclopentanones. Control experiments and DFT analysis of reaction mechanism support a radical mediated pathway and provide a rationale for the observed diastereoselectivity. To the authors’ knowledge, these are the first examples of the use of geminal diboryl group as an activator of VCP ring opening and cycloaddition reaction of α-boryl radicals.
KW - cycloaddition
KW - geminal diborons
KW - thiyl catalysis
KW - vinyl cyclopropane
KW - α-boryl radicals
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U2 - 10.1002/chem.202303175
DO - 10.1002/chem.202303175
M3 - Article
C2 - 37793067
AN - SCOPUS:85176549918
SN - 0947-6539
VL - 30
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 2
M1 - e202303175
ER -