ASYMMETRIC REDUCTIONS VIA TRIALKYLBORANES

手性在有机和生物有机化学中起着核心作用。因此 光学活性化合物的合成是一项重要的工作。我们 发现了某些B-烷基-9-硼双环[3.3.1]壬烷(9-BBN)还原 醛和炔基酮在非常温和的条件下。这个 从α-蒎烯和9-BBN衍生的试剂诱导高度的 光学活性进入酒精产品。例如 苯甲醛-α-d和4-甲基-1-戊炔-3-酮被还原为 具有基本完全不对称诱导的相应醇。 机械论研究表明，这些反应是通过 六中心循环过程而不是脱氢-硼化还原 进程。对于其他酮，如苯乙酮， 脱氢硼化还原工艺变得非常重要。通过运行 在高压下反应，可以完全抑制脱氢硼反应。 并且可以有效地降低各种酮的含量。它已经找到了 手性酮可以在反克拉姆意义上被还原 二烷基硼烷。将探讨这些削减的范围。一个 提供高达80%e.E.的不对称诱导的硼氢化物试剂。 已经被开发出来。将对这种试剂的新类似物进行测试和 机械论研究开始了。光学活性胺的合成， 通过亚胺或亚胺的不对称还原生成氨基醇和氨基酸 二烯与亚胺和取代酮的环合反应 将探索醛类化合物。[2，3]Wittig的立体化学 重排已被阐明。该反应的机理研究 将开始解释观察到的立体选择性的差异 从E和Z开始的材料。这次重新安排的范围将是 探索过了。光学活性叔醇的合成 烷氧基醛的环缩合反应和不对称加成反应 将对炔丙基酮进行研究。

Chirality plays a central role in organic and bioorganic chemistry. Hence the synthesis of optically-active compounds is an important endeavor. We have found certain B-alkyl-9-borabiocyclo [3.3.1]nonanes(9-BBN) reduce aldehydes and alkynyl ketones under remarkably mild conditions. The reagent derived from Alpha-pinene and 9-BBN induces a high degree of optical activity into the alcohol product. For example benzaldehyde-Alpha-d and 4-methyl-1-pentyne-3-one are reduced to the corresponding alcohols with essentially complete asymmetric induction. Mechanistic investigations have shown that these reactions proceed via a six-centered cyclic process rather than a dehydroboration-reduction process. For other ketones, such as acetophenone, the dehydroboration-reduction process becomes important. By running the reaction at high pressure, the dehydroboration may be completely suppressed and a variety of ketones may be effectively reduced. It has been found that chiral ketones may be reduced in ananti-Cram sense with dialkylboranes. The scope of these reductions will be explored. A borohydride reagent which provides asymmetric inductions of up to 80% e.e. has been developed. New analogs of this reagent will be tested and mechanistic studies initiated. The synthesis of optically-active amines, amino alcohols and amino acids via the asymmetric reduction of imines or the cyclocondensation of dienes with imines and substituted ketones or aldehydes will be explored. The stereochemistry of [2,3]Wittig rearrangements has been elucidated. Mechanistic studies on this reaction will be initiated to explain differences in stereoselectivities observed from E and Z starting materials. The scope of this rearrangement will be explored. The synthesis of optically-active tertiary alcohols by cyclocondensations of alkoyx aldehydes and by asymmetric additions to propargyl ketones will be investigates.