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161.
Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid 1, five aldehydes and two isocyanides were reacted both in methanol and in water to prepare a 10-membered β-lactam library via a Ugi-4-centre-3-component reaction. The yields were found to be similar in water and methanol. The diastereoselectivities of the aqueous reactions were similar, though in a few cases higher than those in methanol. The benefits of water are the facile isolation of the precipitated product and the shorter reaction time. 相似文献
162.
Reaction of camphor-derived exo-formyl [2.2.1]bicyclic carbinol with various alkyl primary amines gave regio- and stereo-specific [3.2.1]bicyclic α-amino ketones. A detailed mechanism of the reaction was discussed. This reaction was further applied to the preparation of some camphor-derived oxazaborolidines, one of which proved to be an efficient chiral catalyst for the asymmetric borane reduction of prochiral aryl ketones at room temperature. 相似文献
163.
An eigenvalue of a graph is main if it has an eigenvector, the sum of whose entries is not equal to zero. Extending previous results of Hagos and Hou et al. we obtain two conditions for graphs with given main eigenvalues. All trees and connected unicyclic graphs with exactly two main eigenvalues were characterized by Hou et al. Extending their results, we determine all bicyclic connected graphs with exactly two main eigenvalues. 相似文献