南开大学物理有机化学.pdfVIP

Welcome to Advanced Organic Chemistry The whole art of teaching is only the art of awakening the natural curiosity of young minds for the purpose of satisfying it afterwards. An Unexpected Role of a Trace Amount of Water in Catalyzing Proton Transfer in Phosphine-Catalyzed (3 + 2) Cycloaddition of Allenoates and Alkenes Yuanzhi Xia, Yong Liang, Yuanyuan Chen, Ming Wang, Lei Jiao, Feng Huang, Song Liu, Yahong Li, and Zhi-Xiang Yu* J. Am. Chem. Soc., 2007, 129 (12), 3470-3471 zwitterionic intermediate zwitterionic intermediate The Lu (3 + 2) cycloaddition is also efficient for the synthesis of five-membered heterocycles if imines are used as dipolarophiles. Through elegant work in the groups of Zhang and Fu, asymmetric versions of the Lu (3 + 2) cycloaddition have been developed. Applications of the Lu (3 + 2) cycloaddition to the total synthesis of natural products have also been documented by Lu, Krische, and Pyne, respectively. Further elegant evelopments and extensions of the chemistry of allene-PR3 have been widely pursued by many other groups as well. In conclusion, the Lu (3 + 2) cycloaddition has been investigated with joint forces of computation and experiment . The formation of a 1,3-dipole is slightly exothermic, and the subsequent (3 + 2) cycloaddition is a stepwise process with an activation free energy of 28.3 kcal/mol. The generally accepted intramolecular [1,2] proton shift in the Lu reaction is not possible owing to the very high activation barrier of 39.6 kcal/mol required for this process. Calculations and experiments revealed that water assists this process with an activation free energy of 7.7 kcal/mol. The discovery of the catalytic role of a trace amount of water in the Lu reaction suggests that a trace amount of water could also act as a catalyst in some other “anhydrous” reactions involving [1,2] or [1,n] proton shifts. Intermediates w