Selectivity Control in Alkylidene Carbene-Mediated C−H Insertion and Allene Formation

• Published in: Journal of organic chemistry Vol. 76; no. 4; pp. 1086 - 1099
• Main Authors: Zheng, Jun-Cheng, Yun, Sang Young, Sun, Chunrui, Lee, Nam-Kyu, Lee, Daesung
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 18.02.2011; Amer Chemical Soc
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Chemistry, Organic; Exact sciences and technology; Free radicals chemistry; Organic chemistry; Physical Sciences; Preparations and properties; Reactivity and mechanisms; Science & Technology; ORGANIC-SYNTHESIS; ASYMMETRIC-SYNTHESIS; DIASTEREOSELECTIVE SYNTHESIS; ENANTIOSELECTIVE SYNTHESIS; IMINO ENE REACTION; PROPARGYLIC ALCOHOLS; LITHIUM TRIMETHYLSILYLDIAZOMETHANE; POTASSIUM TERT-BUTOXIDE; AXIALLY CHIRAL ALLENYLSILANES; ALPHA-SULFONYL CARBANIONS; Molecular rigidity; Cyclohexane derivatives; Regioselectivity; Carbon-hydrogen bond; Chemoselectivity; Chemical bond; Competitive reaction; Selectivity; Carbene; Cyclic compound; Steric effect; Organic free biradical; Electronic effect; Intermolecular reaction; Allenic compound; Ethylenic compound; Conformation
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo102180f

Regioselectivity of alkylidene carbene-mediated C−H insertion was explored utilizing electronic, conformational, steric, and stereoelectronic effects. Relying on these factors, highly regio- and chemoselective carbene insertion reaction of C−H bonds in different environments could be obtained. The observed selectivity clearly indicates that an electronic effect plays a more important role than steric effect. In general, C−H bonds in conformationally rigid cyclic environments are less reactive than those in acyclic systems toward carbene insertion, and in this situation, a competing intermolecular reaction between alkylidene carbene and trimethylsilyldiazomethane led to the formation of allenylsilanes. The formation of allenylsilane becomes more favorable as the concentration of reaction becomes higher, as well as the C−H bonds undergoing insertion becomes electronically and conformationally deactivated.