Ring-opening of Isoxazolidine Nucleus by Trimethyl Posphate Treatment: Formation of Tertiary Allylic Alcohols via Intermediate 1,3-Oxazinium Salts
摘要:
5,5-Disubstituted isoxazolidines undergo ring opening reaction, leading to tertiary allylic alcohols, by sequential treatment with trimethyl phosphate (TMP) and NaH. The reaction proceeds through sequence steps which involve an initial alkylation to isoxazolidinium intermediate, followed by ring expansion to tetrahydro-1,3-oxazine, further alkylation and a Hofmann-like elimination towards the final products promoted by NaH.
Asymmetric “Acetylenic” [3+2] Cycloaddition of Nitrones Catalyzed by Cationic Chiral Pd<sup>II</sup>
Lewis Acid
作者:Kazuya Honda、Koichi Mikami
DOI:10.1002/asia.201801016
日期:2018.10.4
Highly enantioselective [3+2] cycloaddition of ynones and nitrones has been developed. Very bulky ligand, DTBM‐SEGPHOS, was used for an effective asymmetric induction over distal reaction centers on the linear ynone dipolarophile and for prevention of PdII catalyst deactivation by coordination of the nitrones. The reaction has wide scope of substrates in both ynones and nitrones.
作者:Evelina Colacino、Pierrick Nun、Francesco Maria Colacino、Jean Martinez、Frédéric Lamaty
DOI:10.1016/j.tet.2008.03.091
日期:2008.6
13C MAS nuclear magnetic resonance experiments. We have also studied the temperature profile during the reaction. A comparative study with the corresponding solvent-free microwave activated reaction showed the superiority of the ball-milling method; 31 examples are described, including the synthesis of the anti-aging agent C-phenyl-N-tert-butyl nitrone (PBN) and one of its analogues C-2-pyridyl-N-tert-butylnitrone
(3 + 3) Cycloaddition of Oxyallyl Cations with Nitrones: Diastereoselective Access to 1,2-Oxazinanes
作者:Marie Cordier、Alexis Archambeau
DOI:10.1021/acs.orglett.8b00617
日期:2018.4.20
Oxyallylcations are prepared in situ from readily available α-tosyloxy ketones and act as transient electrophilic partners in (3 + 3) cycloaddition with nitrones. Under mild conditions, this method provides a chemoselective and diastereoselective route to polysubstituted 1,2-oxazinanes. A stepwise process is proposed to rationalize the diastereoselectivity of this transformation.
Regio‐ and Enantioselective (3+3) Cycloaddition of Nitrones with 2‐Indolylmethanols Enabled by Cooperative Organocatalysis
作者:Tian‐Zhen Li、Si‐Jia Liu、Yu‐Wen Sun、Shuang Deng、Wei Tan、Yinchun Jiao、Yu‐Chen Zhang、Feng Shi
DOI:10.1002/anie.202011267
日期:2021.2
regiospecificity. This approach enabled not only the first organocatalytic asymmetric (3+3) cycloaddition of nitrones but also the first C3‐nucleophilic asymmetric (3+3) cycloaddition of 2‐indolylmethanols. More importantly, theoretical calculations elucidated the role of the cocatalyst HFIP in helping CPA control the reactivity and enantioselectivity of the reaction, demonstrating a new mode of cooperative catalysis
Electronic effects in 1,3-dipolar cycloaddition reactions of N-alkyl and N-benzyl nitrones with dipolarophiles
作者:Andrei Bădoiu、E. Peter Kündig
DOI:10.1039/c1ob06144e
日期:——
1,3-Dipolar cycloadditions afforded fast access to isoxazolidines bearing N-alkyl or N-benzyl substituents. The electronic properties of the substituents in the nitrones define the activity of the dipoles and modulate diastereoselectivity in the non-catalyzed reactions. Using a chiral one-point binding ruthenium Lewis acid catalyst, products were obtained in good yields and with excellent regio-, diastereo-