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2004
Amino acids
U 0400
Towards Functionalized Silicon-Containing α-Amino Acids: Asymmetric Syntheof Sila Analogues of Homoserine and Homomethionine. — Two approaches
49- 175 ses
towards title silicon-containing α-amino acids (XIV) and (XIX) are presented starting
from auxiliary-bearing halomethylsilylpropionic amides (I) or (VII). The methods involve functionalization of the halomethyl group at the silicon followed by asymmetric
α-bromination of the amide or vice versa. The low reactivity of the halomethylsilyl
group is the main difficulty of both pathways since only a few nucleophiles like tetramethylguanidinium azide or sodium phthalimide afford the expected substitution products. Additionally, better stereoselectivity in the α-bromination step is achieved when
the chloromethyl group at silicon is intact [cf. (V) vs. (X)]. Removal of the auxiliary
after introduction of two azide groups followed by hydrogenation of the azide then
gives the amino acid derivatives. The reasons for the generation of a hydroxy group at
the silicon in compound (XIV) [instead of formation of amino acid (XV)] are not clear.
— (SMITH, R. J.; BIENZ*, S.; Helv. Chim. Acta 87 (2004) 7, 1681-1696;
Org.-Chem. Inst., Univ. Zuerich, CH-8057 Zuerich, Switz.; Eng.) — Mischke
2004
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