Amino Acids and Peptides; 70.¹Optically Active α-Amino Acids,N-Boc-Aminoaldehydes and α-Amino-β-hydroxy Acid from 2,3-Epoxy Alcohols

Five-membered oxaza heterocyclic compounds on the basis of epoxides and aziridines

“…The chiral cagelike fragment in 152 can act as asymmetric inductor. Many analogous reactions with trichloroacetonitrile were reported over the past decade [13,191,192]. The reactions of disubstituted oxirane 153 with trichloroacetonitrile were substantially regioselective.…”

“…Dihydrooxazoles 157 and 158 were isolated as intermediate products in syntheses of complex natural compounds [13] (Scheme 93). The effect of the catalyst (Et 2 O · BF 3 , CH 3 SO 3 H, SnCl 4 ) on the reactions of hydroxymethyloxiranes with trichloroacetonitrile, leading to heterocyclization products 159 and 160 (R 1 = H, Pr, i-Bu, C≡CH; R 2 = H, Me, Pr), was studied [192] (Scheme 94). Fluorinated epoxides 161 (R 1 F , R 2 F = CF 3 , C 2 F 5 , C 3 F 7 ) reacted with urea in dioxane to produce fluoroalkyl-substituted 2-aminodihydrooxazoles [193] (Scheme 95 .0]octane-3,7-diones 162 provided that the urea-tooxirane ratio was increased to 3 : 1 (Scheme 96).…”

Synthesis of α‐Ethynyl Glycines

“…[54] Later, Schmidt et al developed a procedure for the synthesis of optically active α-amino acids from 3-ethynyl-substituted epoxides 98b. [55] These substrates, when exposed to a catalytic amount of BF 3 ·Et 2 O, underwent a regioselective aminolysis with an inversion of configuration to provide enantioenriched dihydrooxazines 99b, which contain a C-quaternary stereocenter. 1,3-Dihydrooxazines 99b were hydrolyzed into amino alcohols 100b, which were then converted into the corresponding amino acid derivatives 101b by using a three-step sequence that involving diol cleavage by treatment with NaIO 4 , a Pinnick oxidation, and esterification reactions.…”

Synthesis of Salinosporamide A and Its Analogs as 20S Proteasome Inhibitors and SAR Summarization

“…They described totally three routes to -methylenelactam (40) [51,52] and its analogs [53]. with methyl pyroglutamate (34).…”

“…The selective protection of primary hydroxyl with benzyl group was investigated and the result showed that 2-benzyloxy-1-methylpyridinium triflate was a selective and mild benzylating agent. In the existence of MgO, (S)-41 succeed to afford (S)-44 which was converted into 40 by following the reported procedures [51].…”