Tandem diazotization Heck reactions: A general synthesis of substituted styrenes from anilines

Aromatic substitutions of arenediazonium salts via metal catalysis, single electron transfer, and weak base mediation

Radical aromatic substitutions of arenediazonium salts can be initiated by various methods. The recent developments of weak base-mediated protocols provide great advantages over conventional metal-mediated or photoredox reactions by their operational simplicity, price, hazard potential and scalability.

Palladium-catalyzed 1,1-difunctionalization of ethylene

The 1,1-difunctionalization of ethylene, with aryl/vinyl/heteroaryl transmetalating agents and vinyl electrophiles, is reported. The reaction is high-yielding under a low pressure of ethylene, and regioselectivity is generally high for the 1,1-disubstituted product. The process is highlighted by the use of heteroaromatic cross-coupling reagents, which have not been competent reaction partners in previously reported efforts.

First Heck reaction with arenediazonium cations with recovery of Pd-triolefinic macrocyclic catalyst

The air- and moisture-stable phosphine-free palladium(0) complex 1 is a highly active and recoverable catalyst for Heck olefination of aryl diazonium tetrafluoroborates. The reactions were performed under aerobic conditions at room temperature to give the coupling products in excellent yields. [reaction: see text]

The Heck reaction in the production of fine chemicals

An overview is given of the use of the Heck reaction for the production of fine chemicals. Five commercial products have been identified that are produced on a scale in excess of 1 ton/year. The herbicide Prosulfuron(tm) is produced via a Matsuda reaction of 2-sulfonatobenzenediazonium on 3,3,3-trifluoropropene. The sunscreen agent 2-ethylhexyl p-methoxy-cinnamate has been produced on pilot scale using Pd/C as catalyst. Naproxen(tm) is produced via the Heck reaction of 2-bromo-6-methoxy-naphthalene on ethylene, followed by carbonylation of the product. Monomers for coatings are produced via a Heck reaction on 2-bromo-benzocyclobutene. A key step in the production of the antiasthma agent Singulair(tm) is the use of the Heck reaction of methyl 2-iodo-benzoate on allylic alcohol (18) to give ketone (20). The high cost of palladium has spurred much research aimed at the development of more active palladium catalysts. Ligandless catalysts are very attractive for production, but work only on reactive substrates. Palladacycles are much more stable than Pd-phosphine complexes and can be used at higher temperatures. The same effect has been reached with pincer ligands. Bulky ligands lead to coordinatively unsaturated Pd-complexes, which are highly active for the Heck reaction. Recycle of palladium catalysts is also very important to reduce cost. Immobilization of catalysts by attaching ligands to solid support is not very useful, because of leaching and reduced activity. In ligandless Heck reactions the catalyst can be precipitated on carriers such as silica, dicalite, or celite. This material can be restored to its original activity by treatment with I2 or Br2.Key words: homogeneous catalysis, palladium, arylation, olefination, ligandless, catalyst recycle.