N-Boc-aminals as easily accessible precursors for less accessible N-Boc-imines: facile synthesis of optically active propargylamine derivatives using Mannich-type reactions
We developed a facile and practical synthesis of N-Boc-aminals, which can be used as precursors for less accessible N-Boc-imines. Aminals were obtained via simple dehydration condensation reactions of t-butyl carbamate (BocNH2) and various aldehydes in acetic anhydride, followed by filtration and washing with hexane. The obtained N-Boc-alkynylaminals could be successfully applied in enantioselective
Crafty aminals: The in situgeneration of hitherto unattainable alkynyl‐substituted N‐Boc‐protected imines was realized by the acid‐catalyzed elimination of tert‐butyl carbamate from N‐Boc aminals. A wide variety of N‐Boc imines can be generated, which can then be utilized for subsequent carbon–carbon bond‐forming reactions, such as Mannich‐type reactions.
Direct Mannich-Type Reactions Promoted by Frustrated Lewis Acid/Brønsted Base Catalysts
作者:Jessica Z. Chan、Wenzhi Yao、Brian T. Hastings、Charles K. Lok、Masayuki Wasa
DOI:10.1002/anie.201608583
日期:2016.10.24
Direct Mannich‐type reactions that afford both α‐ and β‐amino esters by the reaction of a broad range of carbonyl compounds and aldimines are disclosed. The transformation is promoted by a sterically frustrated Lewis acid/Brønsted base pair, which is proposed to operate cooperatively: Within the catalyst complex, an enolate is generated that then reacts with a hydrogen‐bond‐activated imine. Noncovalent
Bismuth triflate was found to be an efficient catalyst in the Mannich-typereaction of silylenolates with N-alkoxycarbonylamino sulfones. The reaction proceeded smoothly with a low catalyst loading of bismuth triflate (0.5–1.0 mol %) to afford the corresponding protected β-aminocarbonyl compound in very good yields (up to 96 %).
An enantioselective Brønsted acid catalyzed enamine Mannich reaction
作者:A. Louise Tillman、Darren J. Dixon
DOI:10.1039/b616143j
日期:——
An enantioselective Bronsted acid catalyzed Mannich reaction between acetophenone derived enamines and N-Boc imines has been developed. Simple diol (S)-H(8)-BINOL has been identified as the optimal catalyst, to afford versatile beta-amino aryl ketones in good yield and enantiomeric excess.