Evolution and synthetic applications of the Heck–Matsuda reaction : the return of arenediazonium salts to prominence.

Abstract

This review highlights the potential and the versatility of arenediazonium salts as viable alternatives to conventional aryl halides and oxygen-based electrophiles for Pd-catalyzed Heck reactions. It also presents an overview of the field over the last decade, including some historical perspective of the Heck–Matsuda (HM) reaction with general considerations regarding reaction conditions, type of catalysts used, and the application of arenediazonium salts as reagents for the HM arylation of several types of alkenes. Throughout this review, the principal aspects related to reactivity and selectivity are discussed, and when applicable a comparison is made between the HM and the conventional Heck reactions. Onepot procedures that involve generation of the arenediazonium salt in situ from the corresponding aniline have been 1. Introduction In 1968, Richard F. Heck, then working at the Research Center of Hercules, Inc., USA, reported in a series of six consecutive papers, the palladium-mediated coupling of organomercury compounds to different olefins.[1] In most cases, Heck used stoichiometric amounts of palladium, but following these initial results, he also demonstrated that this transformation could be achieved with a catalytic amount of Li2PdCl4 (1 mol-%) when conducted in the presence of a slight excess of CuCl2.[1a] However, this new methodology developed by Heck drew little attention from the chemical community at that time, mainly because of the use of toxic organomercury compounds, as well as the employment of equimolar amounts of the relatively expensive transition metal palladium. In 1971, Tsutomu Mizoroki in Japan, aware of the potential of this synthetic process, reported the first example of this reaction using aryl iodides.[2] Soon after (1972), Heck also proposed a catalytic version for the process, replacing the arylmercury compounds by aryl halides, but under milder conditions than those described by Mizoroki.[3] This way, the now well-known Heck–Mizoroki reaction was born. [a] Instituto de Química, Universidade Estadual de Campinas, UNICAMP, C.P. 6154, CEP. 13084-971, Campinas, São Paulo, Brazil Fax: +55-19-37883023 E-mail: roque@iqm.unicamp.br Eur. J. Org. Chem. 2011, 1403–1428 © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1403 presented as well as some useful heterogeneous catalytic protocols. Allylic alcohols, conjugated alkenes, unsaturated heterocycles, and unactivated alkenes are capable of being arylated with arenediazonium salts by using simple catalysts such as Pd(OAc)2 or Pd2(dba)3 at room temperature in air and in benign and conventional solvents. In addition to the intramolecular variant of the HM reaction, intermolecular tandem coupling–cyclization processes have also been developed for the construction of a range of oxygen and nitrogen heterocycles. Finally, several applications towards the total synthesis of biologically active natural and nonnatural compounds are highlighted as well as the use of the HM reaction in the synthesis of new chiral, nonracemic ligands.