An experimental and computational approach to understanding the reactions of acyl nitroso compounds in [4+2]-cycloadditions

Chaiyaveij, D.; Batsanov, A.S.; Fox, M.A.; Marder, T.B.; Whiting, A.

Abstract

Catalytic aerobic oxidation of phenyl hydroxycarbamate 1 and 1-hydroxy-3-phenylurea 2 using CuCl2 and 2-ethyl-2-oxazoline in methanol gave acyl nitroso species in situ, which were trapped in nitroso-Diels–Alder (NDA) reactions with various dienes to afford the corresponding cycloadducts in high yields (90–98%). Competing ene products were also present for dienes containing both alkene π-bonds and allylic σ-bonds, and the ene yields are higher with 1 than with 2. The use of the chiral hydroxamic acid, (R)-1-hydroxy-3-(1-phenylethylurea) 3 (same conditions) gave NDA cycloadducts in high yields (97–99%) with no ene product from 2,3-dimethyl-1,3-butadiene. NDA cycloadducts were not obtained from other hydroxamic acid analogues [RCONHOH (R = PhCH2 4; Ph(CH2)2 5; Ph(CH2)3 6; Ph(CH2)4 7; Ph 8; 2-pyridyl 9; 3-pyridyl 10] with various dienes using copper-oxidation but rather were obtained using sodium periodate, resulting in variable NDA yields (13–51%) from hydroxamic acids 1–10 with cyclohexa-1,3-diene and 2,3-dimethyl-1,3-butadiene (several cycloadducts characterized by X-ray crystallography). The NDA and nitroso-ene reaction pathways of nitroso intermediates with dienes were mapped by DFT computations (B3LYP/6-31G*), which showed that the acyl nitroso species are super-reactive and that activation energies in the NDA processes are lower than the isomerization barriers between some cis- and trans-butadienes.

Citation

Chaiyaveij, D., Batsanov, A., Fox, M., Marder, T., & Whiting, A. (2015). An experimental and computational approach to understanding the reactions of acyl nitroso compounds in [4+2]-cycloadditions. Journal of Organic Chemistry, 80(19), 9518-9534. https://doi.org/10.1021/acs.joc.5b01470

• Journal Article Type: Article
• Acceptance Date: Sep 4, 2015
• Publication Date: Oct 2, 2015
• Deposit Date: Sep 24, 2015
• Publicly Available Date: Sep 4, 2016
• Journal: Journal of Organic Chemistry
• Print ISSN: 0022-3263
• Electronic ISSN: 1520-6904
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 80
• Issue: 19
• Pages: 9518-9534
• DOI: https://doi.org/10.1021/acs.joc.5b01470
• Public URL: https://durham-repository.worktribe.com/output/1402089