Catalytic reactions involving heterocycles

In addition to bromides and iodides, the reaction has been successfully extended to chlorides,163 triflates,164 and nonafluorobutanesulfonates (nonaflates).165 These reaction conditions permit substitution in both electron-poor and electron-rich aryl systems by a variety of nitrogen nucleophiles, including alkyl or aryl amines and heterocycles. These reactions proceed via a catalytic cycle involving Pd(0) and Pd(II) intermediates. 

In 1993, we reported that various unsaturated heterocycles can be alkylated with Et-, wPr- and nBuMgCl in the presence of optically pure (EBTHI)ZrCl2 (3a) or (EBTHI)Zr-binol (3b) to afford the derived unsaturated products in >90% ee (cf. 5 6, Scheme 2) [4a]. Many of the simpler five- and six-membered starting materials are available commercially or can be prepared by established procedures. In contrast, catalytic enantioselective reactions involving unsaturated medium ring hetero cycles were not a trivial undertaking the synthesis of these olefinic substrates, by the extant methods, was prohibitively cumbersome. 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

In neutral medium the deuterium solvent isotope effect, (A h2o/ D2o) in the hydrolysis of diaryldiacyloxyspirosulphuranes483, 404-407 has been found to be 1.66. In acidic medium the ratio of catalytic rate constants has been found to be 0.56. Heterocondensed imidazoles 408, are produced in the reaction of N-benzylamides, 409, of nitrogen heterocyclic carboxylic acids with phosphorus pentachloride. Deuterium labelling experiments have been carried out to understand the mechanism of this reaction involving a nitrile ylide species484. 

The case studies below will provide selected examples of calorimetric studies carried out on metal-ligand exchange reactions of phosphorous-based ligands (such as phosphines, phosphite, A -pyrrolyl-phosphines) and N-heterocyclic carbene ligands (NHCs) as well as addition reactions relevant to catalytic transformations, involving metals such as ruthenium, rhodium,platinum,and molybdenum. ... 

Asymmetric catalytic hetero Diels-Alder reactions give access to synthetically important substituted heterocycles [45]. Asymmetric oxa Diels-Alder reactions involving aldehydes and ketones and catalyzed by chiral Lewis acid catalysts can be performed with a high degree of chiral induction [46]. The field is much less advanced that of the corresponding catalytic enantioselective aza Diels-Alder reactions. 

Heterocyclic imidazolylidene carbenes proved to be very interesting ligands of transition metal complexes. Their electronic properties have very often been compared to those of basic phosphines. They are indeed good a-donors but weak n-acceptors. A number of carbene complexes have been involved in catalytic reactions such as metathesis (Ru) or C-C coupling (Pd, Ni). They can be generated easily by deprotonation of an imidazoUum salt in the presence of an organic base. 

Recent advances in catalytic sequential reactions involving hydroelement addition to carbon—carbon multiple bonds 13CRV6864. Recent advances in the Willgerodt—Kindler reaction, particularly, in the synthesis of heterocycles 13CSR7870. 

---