Synthesis of Optically Active 2-Alkoxy-2<i>H</i>-pyran-3(6<i>H</i>)-ones. Their Use as Dienophiles in Diels−Alder Cycloadditions
作者:Christian A. Iriarte Capaccio、Oscar Varela
DOI:10.1021/jo0106896
日期:2001.12.1
cycloadducts 9a-c and 10a were respectively obtained with good diastereofacial selectivity (>80%). Optimized Lewis acid promoted cycloadditions led to 9a-d and 10a,c in higher yields (approximately 80%) and with higher diastereoselectivities (>94%). The major products were formed by approach of the dienes from the less hindered face of the dihydropyranones, and the minor products (such as 11a) were formed
通过氯化锡(IV)促进的糖基化和2-乙酰氧基-3,4-二-的重排,一步合成了光学活性的2-烷氧基-2H-吡喃-3(6H)-一(4a-d)。由D-木糖(1)制备的O-乙酰基-D-木糖醛(3)。通过将二氢吡喃酮4a和4b化学转化为已知的烷基戊吡喃糖苷(分别为7a和7b)来确定C-2处新立体中心的绝对构型。同样,从使用手性位移试剂的(1)H NMR实验中,确定了4a(> 86%)和4b(> 77%)的对映体过量。通过3与手性2-辛醇(分别为R和S)反应获得对映体纯的4c和4d。二氢吡喃酮4a-d在与2,3-二甲基丁二烯和丁二烯的Diels-Alder环加成中用作亲二烯体。在热条件下 仅以良好的非对面选择性(> 80%)分别获得中等产率(约50%)的环加合物9a-c和10a。优化的路易斯酸促进的环加成反应导致9a-d和10a,c的产率更高(约80%),非对映选择性更高(> 94%)。主要产物是由二