[Co(TPP)]‐Catalyzed Formation of Substituted Piperidines

Radical cyclization via cobalt(III)‐carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five‐membered N‐heterocyclic pyrrolidines catalyzed by CoII porphyrins, the [Co(TPP)]‐catalyzed formation of useful si...

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Vydáno v:	Chemistry : a European journal Ročník 25; číslo 22; s. 5658 - 5663
Hlavní autoři:	Lankelma, Marianne, Olivares, Astrid M., de Bruin, Bas
Médium:	Journal Article
Jazyk:	angličtina
Vydáno:	WEINHEIM Wiley 17.04.2019 Wiley Subscription Services, Inc John Wiley and Sons Inc
Témata:	Aldehydes Alkenes Chemistry Chemistry, Multidisciplinary Cobalt Communication Communications C−C coupling C−H activation homogeneous catalysis Intermediates Mathematical analysis nitrogen heterocycles Physical Sciences Porphyrins radicals Science & Technology C-C coupling CATALYSIS C-H activation homogeneous catalysis radicals nitrogen heterocycles CONSTRUCTION CYCLOPROPANATION COBALT(II) INDOLINES CARBENE RADICALS CYCLIZATION C−C coupling C−H activation
ISSN:	0947-6539, 1521-3765
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Popis
Shrnutí:	Radical cyclization via cobalt(III)‐carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five‐membered N‐heterocyclic pyrrolidines catalyzed by CoII porphyrins, the [Co(TPP)]‐catalyzed formation of useful six‐membered N‐heterocyclic piperidines directly from linear aldehydes is presented herein. The piperidines were obtained in overall high yields, with linear alkenes being formed as side products in small amounts. A DFT study was performed to gain a deeper mechanistic understanding of the cobalt(II)‐porphyrin‐catalyzed formation of pyrrolidines, piperidines, and linear alkenes. The calculations showed that the alkenes are unlikely to be formed through an expected 1,2‐hydrogen‐atom transfer to the carbene carbon. Instead, the calculations were consistent with a pathway involving benzyl‐radical formation followed by radical‐rebound ring closure to form the piperidines. Competitive 1,5‐hydrogen‐atom transfer from the β‐position to the benzyl radical explained the formation of linear alkenes as side products. Macrocyclic ligands for heterocyclic products: Radical cyclization via cobalt(III)‐carbene radical intermediates is a powerful method for the synthesis of (hetero)cyclic structures. Building on the recently reported synthesis of five‐membered pyrrolidine rings catalyzed by CoII amidoporphyrins, the [Co(TPP)]‐catalyzed (TPP=tetraphenylporphyrin) formation of six‐membered piperidine rings, which was found to be accompanied by formation of small amounts of linear alkenes, is reported herein. A DFT study was also performed to gain a deeper mechanistic understanding.
Bibliografie:	These authors contributed equally to this work. Dedicated to Professor Pablo Espinet on the occasion of his 70th birthday ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14
ISSN:	0947-6539 1521-3765
DOI:	10.1002/chem.201900587