A Facile Preparation of N-(Isopropoxyalkyl) Amides by Generation and Trapping of N-Acyliminium Ions from Ionization-Rearrangement Reactions of N-Triflyloxy Amides
摘要:
A series of hydroxamic acids were converted to N-triflyloxy amides which were heated in 2-propanol to give N-(1-isopropoxyalkyl) amides in high yields. The method is simple, direct, and extremely tolerant of structural diversity both in the N-acyl group, as well as in the 1-isopropoxyalkyl group. N-Alkylation of secondary N-(1-isopropoxyalkyl) amides can be used for converting them to tertiary N-(1-isopropoxyalkyl) amides. N-Acyliminium ions of wide structural diversity can be generated easily from N-(1-isopropoxyalkyl) amides available by this methodology.
Lawesson's reagent for direct thionation of hydroxamic acids: Substituent effects on LR reactivity
作者:Witold Przychodzeń
DOI:10.1002/hc.20259
日期:——
To explore the generality and scope of direct thionation of hydroxamicacids (HAs), the reaction of various structurally diverse HAs with Lawesson's reagent was investigated. The yield of thiohydroxamic acid (THAs) is poor when HAs possess bulky acyl and/or N-substituents, acidic α-hydrogen atoms, or an N-phenyl ring. THAs yields were correlated with Brown sigma parameter. The relative rates of two
Generation of N-acyl iminium ions from ionization-rearrangement reactions of N-triflyloxy amides
作者:Robert V. Hoffman、Naresh K. Nayyar、Jean M. Shankweiler、Bruce W. Klinekole
DOI:10.1016/s0040-4039(00)76872-9
日期:1994.5
N-Triflyloxy amides undergo ionization in refluxing isopropanol to give N-acyliminium ions which can be trapped by addition of allyltrimethylsilane to the reaction mixture. Alternatively they can be converted to N-(isopropoxy)alkyl amides and then back to N-acyliminium ions under a variety of conditions.
Origins of Regioselectivity in the Reactions of .alpha.-Lactams with Nucleophiles
作者:Robert V. Hoffman、Naresh K. Nayyar、Wenting Chen
DOI:10.1021/jo00118a032
日期:1995.6
Regioselectivity in the reaction of alpha-lactams with nucleophiles results from two competing steps. Nucleophilic addition to the carbonyl group of the alpha-lactam, which yields rearranged, acyl-substituted products, is dependent on the nucleophilicity and the concentration of the nucleophile. Ring opening of the alpha-lactam to an ion pair intermediate, which gives nucleophile incorporation at C-2, is dependent on electronic effects of substituents at C-2. Groups which can stabilize positive charge at C-2 speed up ion pair formation, whereas electron-withdrawing groups slow the ring opening and give more carbonyl addition product. These factors are used to control the regioselectivity and produce a series of unsymmetric urea peptide mimetics in high yields and with complete regiochemical control.
Hoffman Robert V., Nayyar Naresh K., J. Org. Chem, 59 (1994) N 13, S 3530-3539