Asymmetric Methoxyselenenylations and Cyclizations with 3-Camphorseleno Electrophiles Containing Oxime Substituents at C-2. Formation of an Unusual Oxaselenazole from an Oxime-Substituted Selenenyl Bromide
作者:Thomas G. Back、Ziad Moussa、Masood Parvez
DOI:10.1021/jo016061c
日期:2002.1.1
in a highly diastereoselective manner. The free oxime 6b was particularly effective in such methoxyselenenylations, giving diastereomeric ratios (d.r.s) ranging from 86:14 to > 98:2. Even cis-disubstituted alkenes, which typically give poor d.r.s in similar additions with other chiral selenium electrophiles, underwent highly stereoselective additions with this reagent. Reductive deselenizations of
二[(1R)-2-氧代-内-3-硼烯基]二硒化物(4)及其苯甲酸酯衍生物5是由相应的已知的2-酮二硒化物1制备的。用溴处理4和5,然后用三氟甲磺酸银处理。甲醇-二氯甲烷,生成相应的亚硒基三氟甲磺酸酯6b和7b。后者的试剂与多种单,二和三取代的烯烃反应,以高度非对映选择性的方式提供相应的1,2-加成产物(β-甲氧基硒化物)。游离肟6b在这种甲氧基硒烯化反应中特别有效,其非对映体比率(drs)为86:14至> 98:2。即使是通常与其他手性硒亲电试剂相似的添加物,通常也会产生较差的dr-顺式二取代的烯烃,也使用该试剂进行了高度立体选择性的添加。由苯乙烯,顺式和反式-二苯乙烯形成的加合物的还原脱硒作用提供了相应的甲基醚,其绝对构型是通过与真实样品进行比较确定的。如预期的那样,使用6b或7b从顺-和反-二苯乙烯中获得的主要对映体具有相反的构型。此外,当用肟6b或苯甲酸酯7b处理时,二苯乙烯的每种几