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Palladium NNC Pincer Complex as an Efficient Catalyst for the Cycloisomerization of Alkynoic Acids
Author(s) -
Conde Nerea,
SanMartin Raul,
Herrero María Teresa,
Domínguez Esther
Publication year - 2016
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201600492
Subject(s) - palladium , chemistry , pincer movement , cycloisomerization , catalysis , triethylamine , enol , nucleophilic substitution , nucleophile , combinatorial chemistry , medicinal chemistry , stereochemistry , photochemistry , organic chemistry
A two‐step (nucleophilic substitution/palladation by oxidative addition) sequence provides a high‐yielding access to a non‐symmetrical palladium NNC pincer complex. A number of terminal and internal alkynoic acids with different substitution patterns at the α‐ and β‐positions are regio‐ and diastereoselectively cycloisomerized to the corresponding exocyclic enol lactones in the presence of exceedingly low amounts of the latter palladium complex, so that unprecedented turnover numbers and frequencies ranging from 1,000,000 to 700,000 and from 41,667 to 9722 h −1 , respectively, are achieved. The optimized protocol, based on the use of a catalytic amount of triethylamine as base, allows an easy real‐time monitoring of the reaction by NMR spectroscopy. Several pieces of evidence in favor of the direct participation of the above pincer complex as the catalyst of the reaction have been gathered from kinetic and poisoning experiments