Expeditious Synthesis of 2,3,6-Trisubstituted 2H-1,3-Oxazin-4(3H)-ones via the Tertiary Amine-Induced Reaction of 2-Diazo-3-oxoalkanals and Imines Under Mild Conditions
Stereoselective control in the Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents: experimental investigation and theoretical rationalization
作者:Hengzhen Qi、Xinyao Li、Jiaxi Xu
DOI:10.1039/c0ob00783h
日期:——
The stereoselectivity of the Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents was investigated experimentally by determination of the product stereochemistry and theoretically via DFT calculations. The results indicate that imines preferentially attack the less sterically hindered exo-side of the ketenes to generate zwitterionic intermediates. Subsequently, for cyclic imines, the intermediates undergo a conrotatory ring closure directly to produce β-lactams, while for linear imines, the imine moiety of the intermediates isomerizes to more stable intermediates, which further undergo a conrotatory ring closure to afford trans-β-lactams. The steric hindrance and the isomerization, rather than the torquoelectronic effect, play crucial roles in controlling the stereoselectivity in the practical Staudinger reactions involving monosubstituted ketenes with electron acceptor substituents, although the unaccessible borylketene with a powerful electron acceptor group controls the stereoselectivity torquoelectronically, in theory.
Gold-catalyzed formal [4π+2π]-cycloadditions of tert-butyl propiolates with aldehydes and ketones to form 4H-1,3-dioxine derivatives
作者:Somnath Narayan Karad、Wei-Kang Chung、Rai-Shung Liu
DOI:10.1039/c5cc04538j
日期:——
Novel gold-catalyzed [4π+2π]-cycloadditions of tert-butyl propiolates with aldehydes and ketones have been developed to form 4H-1,3-dioxine derivatives.
Pd-Catalyzed Carbonylation of Diazo Compounds at Atmospheric Pressure: A Catalytic Approach to Ketenes
作者:Zhenhua Zhang、Yiyang Liu、Lin Ling、Yuxue Li、Yian Dong、Mingxing Gong、Xiaokun Zhao、Yan Zhang、Jianbo Wang
DOI:10.1021/ja107351d
日期:2011.3.30
and affects the diastereoselectivity of the β-lactam products by assisting isomerization of the addition intermediate. On the other hand, the acylketenes generatedfrom the Pd-catalyzed carbonylation of α-diazoketones react with imines in a formal [4 + 2] cycloaddition manner to afford 1,3-dioxin-4-one derivatives. This straightforward carbonylation provides a new approach toward highly efficient catalytic