Bach Jordi, Blachère Cécile, Bull Steven D, Davies Stephen G, Nicholson Rebecca L, Price Paul D, Sanganee Hitesh J, Smith Andrew D
The Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford, UK OX1 3QY.
Org Biomol Chem. 2003 Jun 7;1(11):2001-10. doi: 10.1039/b301119d.
A study of the properties of N-hydrocinnamoyl- derivatives of 5,5-dimethyloxazolidin-2-one, 4,4-dimethyloxazolidin-2-one and oxazolidin-2-one upon hydride reduction with DIBAL-H demonstrates that the 5,5-dimethyl-group is essential for inhibition of endocyclic nucleophilic attack. For instance, treatment of N-hydrocinnamoyl-5,5-dimethyloxazolidin-2-one with DIBAL-H results in the selective formation of the stable N-1'-hydroxyalkyl derivative which may be regarded as a masked hydrocinnamaldehyde equivalent, as treatment under basic conditions affords the parent aldehyde in excellent yield. Treatment of N-hydrocinnamoyl-4,4-dimethyloxazolidin-2-one with DIBAL-H under identical conditions affords a complex mixture of products, including the formate ester product of endocyclic cleavage. As an alternate strategy, DIBAL-H reduction of straight chain and branched N-acyl-5,5-dimethyloxazolidin-2-one derivatives, followed by a Horner-Wadsworth-Emmons reaction affords alpha,beta-unsaturated esters in good yields. Branching alpha- to the exocyclic carbonyl in N-acyl-oxazolidinones inhibits DIBAL-H reduction, but this can be overcome by precomplexation with ZnCl2, with subsequent fragmentation generating either the corresponding aldehyde or alpha,beta-unsaturated esters. The addition of ZnCl2 has been shown to increase the diastereoselectivity observed in Wadsworth-Horner-Emmons reactions of lithiated phosphonates.
一项关于5,5 - 二甲基恶唑烷 - 2 - 酮、4,4 - 二甲基恶唑烷 - 2 - 酮和恶唑烷 - 2 - 酮的N - 氢化肉桂酰衍生物在使用二异丁基氢化铝进行氢化物还原时性质的研究表明，5,5 - 二甲基基团对于抑制环内亲核进攻至关重要。例如，用二异丁基氢化铝处理N - 氢化肉桂酰 - 5,5 - 二甲基恶唑烷 - 2 - 酮会选择性地形成稳定的N - 1'- 羟烷基衍生物，该衍生物可被视为一种掩蔽的氢化肉桂醛等效物，因为在碱性条件下处理能以优异的产率得到母体醛。在相同条件下用二异丁基氢化铝处理N - 氢化肉桂酰 - 4,4 - 二甲基恶唑烷 - 2 - 酮会得到产物的复杂混合物，包括环内裂解的甲酸酯产物。作为一种替代策略，直链和支链的N - 酰基 - 5,5 - 二甲基恶唑烷 - 2 - 酮衍生物经二异丁基氢化铝还原，随后进行霍纳尔 - 沃兹沃思 - 埃蒙斯反应，能以良好的产率得到α,β - 不饱和酯。N - 酰基恶唑烷酮中环外羰基α位的支链会抑制二异丁基氢化铝还原，但这可以通过与氯化锌预络合来克服，随后的裂解会生成相应的醛或α,β - 不饱和酯。已表明添加氯化锌会增加锂化膦酸酯在沃兹沃思 - 霍纳尔 - 埃蒙斯反应中观察到的非对映选择性。
