Benzotriazole-Mediated Stereoselective Olefination of Carboxylic Esters: Transformation of α-Amino Acid Esters into Chiral Allylamines
摘要:
Diastereoselective trans-olefinations of carboxylic esters 3a-h have been accomplished using benzylic or allylic benzotriazole derivatives la-e to prepare alpha-(benzotriazol-1-yl) ketones 4a-i, for the subsequent reduction of 4a-i, and finally for low-valent titanium-effected dehydroxybenzotriazolylation.(1) N-Protected alpha-amino acid esters 9a-c and 15 thus give allylamines 13a-e and 19 with virtually full retention of chirality. Mechanistic aspects of the dehydroxybenzotriazolylation are discussed.
Highly selective enolization method for heteroatom substituted esters; its application to the ireland ester enolate claisen rearrangement
作者:Kouji Hattori、Hisashi Yamamoto
DOI:10.1016/s0040-4020(01)81109-1
日期:1994.3
A method for the stereoselective synthesis of silylketeneacetals from α-siloxy esters, β-hydroxy esters, and α-aminoesters is described. Internal quench with excess trimethylsilyl chloride of the lithium enolate at −100 °C, which is generated using a hindered base, LTMP, leads to the selective formation of E-silyl keteneacetal. In contrast, the deprotonation at −100 °C using LHMDS in THF-HMPA (4:1)
N-Bis-trimethylsilylation of alpha-amino acids using the powerful trimethylsilyl triflate reagent is difficult, and is rendered impossible in the case of bulky side-chains (valine). However, favorable entropy changes resulting from a cyclization reaction allow the formation of "benzostabase" N-diprotections regardless of the side-chain bulk.
Hattori Kouji, Yamamoto Hisashi, Tetrahedron, 50 (1994) N 10, S 3099-3112