Crystallization-Induced Asymmetric Transformation vs Quasi-Racemate Formation in Tetravalent Boron Complexes
作者:E. Vedejs、R. W. Chapman、S. Lin、M. Müller、D. R. Powell
DOI:10.1021/ja994023t
日期:2000.4.1
Crystallization-induced asymmetric transformation (AT) has been achieved with the salicaldimine complexes 8/9, 11/12, and 14a/15a and with the oxazaborolidinone complexes 22b/23b and 22c/23c. In the case of 22a and 23a, the initially formed 3.1 mixture of diastereomers crystallizes under equilibrium conditions to afford a quasi-racemate 24, containing both diastereomers in the unit cell. Enolate formation from ent-22b is demonstrated, and methylation occurs to give 26a. Aldol condensation of the enolate is also feasible, and hindered aldehydes afford adducts such as 27a or 27b with good diastereoselectivity. Factors that contribute to quasi-racemate formation are discussed.
Hydroxylamine as an oxygen nucleophile: substitution of sulfonamide by a hydroxyl group in benzothiazole-2-sulfonamides
作者:Jos J. A. G. Kamps、Roman Belle、Jasmin Mecinović
DOI:10.1039/c2ob26929e
日期:——
the corresponding amine. Mechanistic studies that employ a combination of structure–reactivity relationships, oxygen labeling experiments, and (in)direct detection of intermediates and products reveal that the reaction proceeds via oxygen attack, and that oxygen incorporated in the 2-hydroxybenzothiazole product derivesfrom hydroxylamine. The reaction, which is performed under mild conditions, can be