1,4-addition of TMSCCl3to nitroalkenes: efficient reaction conditions and mechanistic understanding

Wu, Na; Wahl, Benoit; Woodward, Simon; Lewis, William

Abstract

Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70 %) and excellent purity. Compounds of the type NBu4X [X=Ph3SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4-additions to a range of cyclic and acyclic nitroalkenes, in THF at 0–25 °C, typically in moderate to excellent yields (37–95 %). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies (1H, 19F, 13C and 29Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13 M) at −20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me3SiF, Ph3SiF and NBu4CCl3. The latter is stable to at least 0 °C and does not add nitroalkene from −20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13 M at −20 °C), when treated with TBAT, leads to immediate formation of the 1,4-addition product, suggesting the reaction proceeds via a transient [Me3Si(alkene)CCl3] species, in which (alkene) indicates an Si⋅⋅⋅O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3− addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4[CH2[DOUBLE BOND]NO2] is an efficient promoter. Use of H2C[DOUBLE BOND]CH(CH2)2CH[DOUBLE BOND]CHNO2 in air affords radical-derived bicyclic products arising from aerobic oxidation.

Citation

Wu, N., Wahl, B., Woodward, S., & Lewis, W. (2014). 1,4-addition of TMSCCl3to nitroalkenes: efficient reaction conditions and mechanistic understanding. Chemistry - A European Journal, 20(25), https://doi.org/10.1002/chem.201402394

• Journal Article Type: Article
• Acceptance Date: May 21, 2014
• Online Publication Date: May 27, 2014
• Publication Date: Jun 16, 2014
• Deposit Date: Sep 29, 2017
• Publicly Available Date: Sep 29, 2017
• Journal: Chemistry - a European Journal
• Print ISSN: 0947-6539
• Electronic ISSN: 1521-3765
• Publisher: Wiley
• Peer Reviewed: Peer Reviewed
• Volume: 20
• Issue: 25
• DOI: https://doi.org/10.1002/chem.201402394
• Keywords: brønsted base catalysis; catalysis; Michael addition; reaction mechanisms; trichloromethylation
• Public URL: https://nottingham-repository.worktribe.com/output/730675
• Publisher URL: http://onlinelibrary.wiley.com/doi/10.1002/chem.201402394/abstract
• Contract Date: Sep 29, 2017