N-Alkyloxycarbonyl-3-aryloxaziridines: Their Preparation, Structure, and Utilization As Electrophilic Amination Reagents
摘要:
AbstractThis paper reports the synthesis of a series of N‐protected oxaziridines (N‐Moc, Boc, Z or Fmoc) and discusses their ability to deliver their N‐alkoxycar‐bonyl fragment to amines, enolates, sulfur, and phosphorus nucleophiles (electrophilic amination). These oxaziridines are prepared by oxidation of the corresponding imines with oxone or anhydrous MCPBA lithium salt as the source of oxygen. They transfer their N‐protected fragment to primary and secondary amines to give protected hydrazines in fair to excellent yield. The nitrogen transfer to free amino acids (in form of their R4N+ salts) is particularly fast, even at low temperature, providing L (or D) N‐protected α‐hydrazino acids. Enolates are C‐aminated to give N‐protected α‐amino ketones, esters, or amides in modest yield, due to a side aldol reaction of the unreacted enolate with the released benzaldehyde. With tertiary amines (Et3N), sulfides (PhSMe), and phosphines (Ph3P), amination and oxidation proceed in a parallel way; the amount of amination product increases when the temperature is lowered (kinetic control). Some of the factors that can orient the oxaziridine reactivity towards amination or oxidation of nucleophiles are considered.
A Highly Enantioselective Mannich-Type Reaction of Glycine Schiff Base Catalyzed by a Cinchoninium Salt
作者:Zhonglin Tao、Arafate Adele、Xiang Wu、Liuzhu Gong
DOI:10.1002/cjoc.201400453
日期:2014.10
A chiral phase‐transfer catalyst, derived from the combination of cinchona alkaloid backbone and BINOL skeleton, enabled a Mannichreaction of glycine Schiff base with N‐Boc‐imines to generate α,β‐diamino acid derivatives in excellent yields (up to 99%) and with high diastereo‐ and enantioselectivities (up to>20:1 dr, 96% ee).
Synthesis of α-Amino Acid Derivatives and Peptides via Enantioselective Addition of Masked Acyl Cyanides to Imines
作者:Kin S. Yang、Viresh H. Rawal
DOI:10.1021/ja510135t
日期:2014.11.19
asymmetric synthesis of amino acid derivatives is reported. Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselectiveadditions to N-Boc-aldimines. The reactions are catalyzed by a modified cinchona alkaloid, which can function as a bifunctional, hydrogen bonding catalyst, and afford adducts in excellent yields (90–98%) and high enantioselectivities (up to 97
N-BOC or N-FMOC benzaldimines are oxidized to the corresponding 3-Aryl-N-BOC or N-FMOC oxaziridines by reaction with Li m-chloroperoxybenzoate under aprotic conditions. The new oxaziridines can transfer their N-BOC or N-FMOC group to morpholine to give the corresponding Nβ-protected hydrazines.