Route for Optically Active Cyclopropanols Utilizing Organoboranes

末端烯基硼酸很容易被发现。酒石酸酯或酒石酸酰胺的。手性修饰的硼酯通过西蒙斯-史密斯程序进行环丙化，具有高的“非对映面分化”。由此产生的环丙基硼酸盐衍生物可以在温和的条件下氧化成相应的光学活性环丙醇。另一方面，内部烯基硼酯不能通过Simmons-Smith反应和其他一些类碳反应顺利地进行环丙化。这些结果表明，这些烯硼酯的a-烷基取代基可能会对过渡态几何结构产生空间干扰。上述得到的旋光性环丙醇在不接触不对称碳中心的情况下，通过先转化为硅醚，然后进行乙酰汞-还原反应，转化为开环产物。此外，具有光学活性的环丙基硼酸盐中间体不仅可以通过氧化反应，还可以通过各种已知的有机硼烷反应转化为各种类型的合成有用的化合物。为了证明这一点，这里应用了与氯溴甲基锂的单碳化反应。该反应后再进行氧化处理，得到相应的光学活性环丙基甲醇衍生物。这些化合物，以前，已被证明可转化为三-2-甲基- 1,3 -烷二醇通过氧化汞还原反应进行区域选择性和立体特异性的方式。因此，烯基硼酯衍生物的不对称环丙化反应提供了具有光学活性的环丙醇和高合成潜力的环丙甲醇。

Terminal alkenylboronic acids were easily es. terified with tartaric esters or amides. The chirally modified boronic esters were then cyclopropanated by the Simmons-Smith procedure with high "diastereoface differentiation. Thus produced cyclopropylboronate derivatives could then be oxidized under mild conditions to the corresponding optically active cyclopropanols. Internal alkenylboronic esters, on the other hand, could not be cyclopropanated smoothly by the Simmons-Smith reaction and some other carbenoid reactions. By these results, it was suggested that the a-alkyl substituent of these alkenyboronic esters might cause steric interference in the transition state geometry. The optically active 'cyclopropanols-obtained above were converted to the ringopened products without touching the asymmetric carbon center at the beta position by first converting to its silyl ether and then subjecting to the acetoxymercuration-demercuration reaction. Furthermore, the optically active cyclopropylboronate intermediates can be converted to various types of synthetically useful compounds not only by the oxidation reaction but also by variety of known reactions of organoboranes. To demonstrate it, here, the onecarbon hbmologation reaction with chlbromethyl-lithium was applied. This reaction followed by oxidative work-up afforded the corresponding optically active cyclopropylmethanol derivatives. These compouids have, previously, been shown to be convertible to threo-2-methyl-1, 3-alkanediols by the oxymercuration-demercuration reaction which proceeds regioselective and stereospecific manner. Therefore, this asymmetric cyclopropanation reaction of alkenylboronic ester derivatives provides optically active cyclopropanols and cyclopropylmethanols of high synthetic potential.