钯催化α,β-不饱和酰氯与炔烃合成环戊烯酮模块化策略机理的密度泛函理论计算

DFT mechanistic insight into the modular strategy involved in the palladium-catalyzed synthesis of cyclopentenones fromα,β-unsaturated acid chlorides and alkynes

环戊烯酮是重要的有机合成原料,也是生物活性化合物和天然产物构建模块。采用密度泛函理论计算,本文研究以硅烷为氢源,钯催化α,β-不饱和酰氯与炔烃合成环戊烯酮的模块化策略的机理。研究表明该反应经下面过程顺序进行:钯催化剂拆分酰氯成烯基、羰基和氯单元;一氧化碳释放;炔烃与烯基偶联;一氧化碳重新配位和迁移插入形成另一个C—C键;经CC双键迁移插入关环,与氢硅烷发生转金属反应,C,H-还原消除释放产物。该机理与实验工作者提出的机理不同,羰基通过在溶剂笼中释放和重新配位参与反应,而不是一直与钯配位。转金属H/Cl交换发生在反应后期,是反应的瓶颈过程,而不是发生在前期的酰氯拆分。

Cyclopentenones are important synthetic building blocks and as motifs appear in bioactive molecules and natural products.We applied density functional theory(DFT)calculations to gain insight into the modular strategy involved in the palladium-catalyzed synthesis of cyclopentenone fromα,β-unsaturated acid chlorides and alkynes in the presence of hydrosilane.The study unveils that the transformation proceeds via the sequence:the disassembly ofα,β-unsaturated acid chloride into vinyl,carbonyl,and Cl fragments with the palladium catalyst;carbon monoxide release;coupling of alkyne with vinyl group;carbon monoxide re-coordination and migratory insertion to form another C—C bond with alkyne,ring-closure via CC bond insertion,transmetalation with hydrosilane,C,H-reductive elimination to release the product.Different from the mechanism proposed by the experimentalists,the CO group is involved in the reaction via separate liberation and re-coordination in the solvent cage,rather than persistent coordination with palladium.The transmetalation for H/Cl exchange takes place at the late stage and is a bottleneck of the transformation,instead of at early disassembly stage.