First Stereoselective Inverse Demand [4 + 2] Cycloaddition Reactions of Novel Chiral Allenamides with Heterodienes. Preparation of Highly Functionalized 2-Arylpyranyl Heterocycles
摘要:
The first stereoselective inverse demand [4 + 2] cycloaddition reactions of chiral allenamides with heterodienes are described here. These reactions lead to stereoselective synthesis of highly functionalized pyranyl heterocycles. A mechanistic model is also proposed here based on the stereochemical assignment and comparisons of stereoselectivities obtained from various chiral allenamides.
Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N-Heterocyclic Carbene-Copper Complex
reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO2. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β‐hydrogen atoms, such as Et2Zn or Bu2Zn, also gave the corresponding alkylative carboxylation products without β‐hydride elimination. The present
NMR Studies on Epoxidations of Allenamides. Evidence for Formation of Nitrogen-Substituted Allene Oxide and Spiro-Epoxide via Trapping Experiments
作者:C. Rameshkumar、Hui Xiong、Michael R. Tracey、Craig R. Berry、Letitia J. Yao、Richard P. Hsung
DOI:10.1021/jo011048d
日期:2002.2.1
the predominant formation of the 3-oxetanone, in the presence of furan, [4 + 3] cycloaddition of the nitrogen-substituted allene oxide or oxyallyl cation with furan occurs faster than the second epoxidation efficiently leading to cycloadducts. This rate difference plays an invaluable role for the success of a stereoselective sequential epoxidation-[4 + 3] cycloaddition reaction via DMDO epoxidations
Efficient preparations of novel ynamides and allenamides
作者:Lin-Li Wei、Jason A. Mulder、Hui Xiong、Craig A. Zificsak、Christopher J. Douglas、Richard P. Hsung
DOI:10.1016/s0040-4020(00)01014-0
日期:2001.1
achiral allenamides, ynamides are prepared from enamides via bromination followed by base-induced elimination of the Z-bromoenamides. These ynamides and allenamides possess improved thermal stability compared to ynamines and allenamines. They can be isolated, purified, and handled with ease, and thus, should be synthetically more useful than traditional ynamines and allenamines.
carboxylation of the resulting alkenylzinc species with CO2. This protocol would be a useful method for the synthesis of α,β‐dehydroamino acid derivatives possessing a functionalized alkyl group due to the high regio‐ and stereoselectivity, simple one‐pot procedure as well as the use of CO2 as a starting material.
Synthesis of amido-spiro[2.2]pentanes via Simmons–Smith cyclopropanation of allenamides
作者:Ting Lu、Ryuji Hayashi、Richard P. Hsung、Kyle A. DeKorver、Andrew G. Lohse、Zhenlei Song、Yu Tang
DOI:10.1039/b908205k
日期:——
Simmons–Smith cyclopropanations of allenamides en route to amido-spiro[2.2]pentanes is described here. While the diastereoselectivity was low when using unsubstituted allenamides, the reaction is overall efficient and general, representing the most direct synthesis of both chemically and biologically interesting amido-spiro[2.2]pentane systems. With α-substituted allenamides, while the diastereoselectivity