Reactivity of pyridines bearing EWG with bis-(TMS)ketene acetals. Substituent-induced lactonization reaction

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• 作者：Alej ; ro Rivera-Hern谩ndez ; Guillermo M. Chans ; Henri Rudler ; Jos茅 G. L贸pez Cort茅s ; R. Alfredo Toscano ; Cecilio 脕lvarez-Toledano
• 关键词：Cyclization ; Pyridines ; Silyl enol ethers ; Nucleophilic additions ; 纬- and 未-Lactones
• 刊名：Tetrahedron
• 出版年：11 March, 2014
• 年：2014
• 卷：70
• 期：10
• 页码：1861-1871
• 全文大小：982 K

文摘

The nucleophilic addition of bis-(TMS)ketene acetals to pyridines substituted by electron-withdrawing groups, activated with triflic anhydride, leads to their corresponding dihydropyridine carboxylic acids in a first instance. These acids can be efficiently turned into new bicyclic lactones by either of three different methods: first, bicyclic 纬-lactones were successfully obtained by an unprecedented Michael-type ring closing procedure assisted by silica gel; second, bicyclic 未-bromolactones were achieved by a NBS-promoted process; and third, the unexpected spontaneous formation of new hydroxy 纬-spirolactones was observed. Along the work presented herein, the scope, limitations, and regioselectivity of these lactonization reactions were studied, confirming the utility of bis-(TMS)ketene acetals as 1,3-dinucleophiles in this type of reactions, extending thus the range of synthesis of a wide variety of new aza-compounds.