TRANSITION-METAL-CATALYZED CYCLIZATION OF ALKYNOIC ACIDS TO ALKYLIDENE LACTONES
TRANSITION-METAL-CATALYZED CYCLIZATION OF ALKYNOIC ACIDS TO ALKYLIDENE LACTONES
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DOI：
10.1021/ja00255a025
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发表时间：
1987-10-14
影响因子：
15
通讯作者：
TAYLOR, NJ
中科院分区：
文献类型：
--
作者：
CHAN, DMT;MARDER, TB;TAYLOR, NJ
本文报道了一种新的Rh（I）配合物[（cycphos）RhCl]_2（4）（cycphos = 1，2-双（二环己基膦基）乙烷）能有效地将炔酸Ⅰ ~ Ⅳ环化为相应的环外烯醇内酯。在室温下，内酯化反应产率较高，二氯甲烷是环化反应的最佳溶剂。观察到Z-烯烃异构体的排他性形成，即，羧酸根OH的反式加成穿过三键。在取代的戊炔酸体系中也强烈偏好形成五元环与六元环。在类似的反应条件下测试了其他富电子的第VIII族过渡金属络合物和汞盐的催化活性，发现效果较差。建议的机制涉及初始OH活化的金属中心，然后由亲核攻击的羧酸根阴离子的金属配位的中间体的炔，和随后的还原消除从所得的双乙烯基络合物释放的内酯产品和再生的催化剂。
Alkynoic acids I-IV can be effectively cyclized to the corresponding exocyclic enol lactones with a new Rh(I) complex, [(cycphos)RhCl]2 (4) (cycphos = 1,2-bis(dicyclohexylphosphino)ethane), that we have developed. The high-yield lactonizations can be performed at room temperature, and methylene chloride appears to be the best solvent for the cyclization. Exclusive formation of Z-olefinic isomers was observed, i.e., trans addition of the carboxylate OH cross the triple bond. There is also a strong preference for the formation of five- vs six-membered rings in the substituted pentynoic acid systems. Other electron-rich group VIII transition-metal complexes and mercuric salts were tested for catalytic activity under similar reaction conditions and were found to be less effective. The proposed mechanism involves initial OH activation by the metal center followed by nucleophilic attack of carboxylate anion on the metal-coordinated alkyne of the intermediate, and subsequent reductive elimination from the resulting hydrido-vinyl complex releases the lactone product and regenerates the catalyst.