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|標題:||Asymmetric Synthesis of alpha-Amino Acids: Preparation and Alkylation of Monocyclic Iminolactones Derived from alpha-Methyl trans-Cinnamaldehyde|
|期刊/報告no：:||Journal of Organic Chemistry, Volume 73, Issue 24, Page(s) 9527-9534.|
|摘要:||Two novel chiral monocyclic iminolactones 14a and 14b have been prepared. The chiral auxiliary 12 was obtained from alpha-methyl-trans-cinnamaldehyde through reduction, methylation, Sharpless asymmetric dihydroxylation, and oxidation in 87% overall yield. Esterification of compound 12 with the respective protected amino acids followed by deprotection and cyclization provided the corresponding iminolactones, each in 82% overall yield. Alkylation of the iminolactone 14a afforded the alpha-methyl-alpha,alpha-disubstituted products 15 and 16 in good yields (78-99%) and excellent diastereoselectivity (de >98%). Alkylations of the iminolactone 14b furnished the alpha-benzyl-alpha,alpha-disubstituted products 15a, 16b, 17, and 18 in good yields (51-86%) but moderate diastereoselectivities (43-56%). When HMPA or DMPU was used as a cosolvent, the rate of alkylation of the iminolactone 14b was accelerated with improved yields (56-99%) and diastereoselectivities (50-83%). Hydrolysis of the dialkylated iminolactones yielded the alpha,alpha-disubstituted a-amino acids in good yields (80-98%) and high enantiomeric excesses (98-99%) with good recovery of compound 12 (83-92%).|
|Appears in Collections:||化學系所|
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