Regiospecific synthesis of 4-deoxy-D-threo-hex-3-enopyranosides by simultaneous activation-elimination of the talopyranoside axial 4-OH with the NaH/Im2SO2 system:: Manifestation of the stereoelectronic effect
Regiospecific synthesis of 4-deoxy-D-threo-hex-3-enopyranosides by simultaneous activation-elimination of the talopyranoside axial 4-OH with the NaH/Im2SO2 system:: Manifestation of the stereoelectronic effect
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DOI：
10.1002/ejoc.200600526
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发表时间：
2006-11-27
影响因子：
2.8
通讯作者：
D'Andrea, Felicia
中科院分区：
文献类型：
--
作者：
Attolino, Emanuele;Catelani, Giorgio;D'Andrea, Felicia
发展了一种区域选择性地制备4-脱氧-和2，4-二脱氧-2-乙酰胺基-β-D-苏式己-3-烯吡喃糖苷的新方法。该方法包括在-30 ℃下通过NaH/N，N '-磺酰基二咪唑系统介导的β-D-Talopyranosides和2-乙酰氨基-2-脱氧-β-D-Talopyranosides的OH-4基团的同时活化-消除。应用于类似的β-D-吡喃半乳糖苷的相同反应在没有任何区域选择性的情况下发生，得到己-3-和己-4-烯吡喃糖苷的混合物。在甲基2，3，6-三-O-苄基-α-D-塔罗-和α-D-吡喃半乳糖苷的情况下，可以通过在-30 ℃下淬灭反应来分离相应的4-O-咪唑基酯。在将这些粗产物加热至室温时，α-talo-4-O-咪唑基酯以非常高的产率得到相应的己-3-烯衍生物，但其α-半乳糖类似物以低的产率得到己-4-烯吡喃糖苷烯醇醚。talo和galacto系列之间的不同区域化学结果归因于立体电子效应，仅在talo构型的化合物中，由轴向布置的C-2电负性取代基施加，其选择性地加速反周面C（3）-H键的断裂。
new and high-yielding method for the regioselective preparation of 4-deoxy- and 2,4-dideoxy-2-acetamido-beta-D-threohex-3-enopyranosides has been developed. The process involves a simultaneous activation-elimination of the OH-4 group of beta-D-talopyranosides and 2-acetamido-2-deoxy-beta-D-talopyranosides, mediated by the NaH/N,N'-sulfuryldiimidazole system at -30 degrees C. The same reaction applied on the analogous beta-D-galactopyranosides takes place without any regioselectivity, affording mixtures of hex-3- and hex-4-enopyranosides. In the case of the methyl 2,3,6-tri-O-benzyl-alpha-D-talo- and alpha-D-galactopyranosides, the corresponding 4-O-imidazylates can be isolated by quenching the reactions at -30 degrees C. Upon warming these crude products to room temperature, the alpha-talo-4-O-imidazylate gives the corresponding hex-3-eno derivative in very high yield, but its a-galacto analogue gives the hex-4-enopyranoside enol ether in poor yield. The different regiochemical outcome between the talo and the galacto series has been attributed to the stereoelectronic effect exerted, exclusively in talo-configured compounds, by the axially disposed C-2 electronegative substituent, which selectively accelerates the breaking of the anti-periplanar C(3)-H bond.