Isoquinolines palladium® chloride

I, 2-Dihydroisoquinolines are reported to be formed when (a) the 1,2,3,4-tetrahydro derivatives are oxidized with oxygen in pyridine solution60 or with palladium chloride,51 (b) when 29 is treated with dry sodium hydroxide,52 or (c) when the benzylaminopropyne [(30) R = H or Me] is heated with polyphosphoric acid.53 When isoquinoline is reduced with sodium in liquid ammonia, one of the products was... 

Phosphonate analogues of Reissert compounds (76) have been prepared and converted into 1-alkyl-isoquinolines (Scheme 49). Treatment of a number of A -methylisocarbostyrils with mercuric acetate gave rise to 4-mercuri-ated derivatives, which underwent insertion reactions with methyl acrylate and with styrenes in the presence of palladium chloride (Heck reaction). 

This method is very useful for the construction of 1-substituted 3,4-dihydroisoquinolines, which if necessary can be oxidized to isoquinolines. A P-phenylethylamine (l-amino-2-phenylethane) is the starting material, and this is usually preformed by reacting an aromatic aldehyde with nitromethane in the presence of sodium methoxide, and allowing the adduct to eliminate methanol and give a P-nitrostyrene (l-nitro-2-phenylethene) (Scheme 3.17). This product is then reduced to the p-phenylethylamine, commonly by the action of lithium aluminium hydride. Once prepared, the p-phenylethylamine is reacted with an acyl chloride and a base to give the corresponding amide (R = H) and then this is cyclized to a 3,4-dihydro-isoquinoline by treatment with either phosphorus pentoxide or phosphorus oxychloride (Scheme 3.18). Finally, aromatization is accomplished by heating the 3,4-dihydroisoquinoline over palladium on charcoal. 

Isoquinoline synthesis Bischler-Napieralski synthesis is used to synthesize isoquinolines. (3-phenylethylamine is acylated, and then cyclodehy-drated using phosphoryl chloride, phosphorus pentoxide or other Lewis acids to yield dihydroisoquinoline, which can be aromatized by dehydrogenation with palladium, for example in the synthesis of papaverine, a pharmacologically active isoquinoline alkaloid. 

As in the Skraup quinoline synthesis, loss of two hydrogen atoms is necessary to reach the fully aromatic system. However, this is usually accomplished in a separate step, utilising palladium catalysis to give generalised isoquinoline 6.14. This is known as the Bischler-Napieralski synthesis. The mechanism probably involves conversion of amide 6.12 to protonated imidoyl chloride 6.15 followed by electrophilic aromatic substitution to give 6.13. (For a similar activation of an amide to an electrophilic species see the Vilsmeier reaction, Chapter 2.)... 

A palladium-catalyzed three-component reaction with 2-iodobenzoyl chloride or methyl 2-iodobenzoate, allene and primary aliphatic or aromatic amines to prepare fV-substituted 4-methylene-3,4-dihydro-1 (27/)-isoquinolin-1 -ones was disclosed <02TL2601>. A synthesis of 1-substituted 1,2,3,4-tetrahydroisoquinolines via a Cp2TiMe2-catalyzed, intramolecular hydroamination/cyclization of aminoalkynes was also reported <02TL3715>. Additionally, a palladium-catalyzed one-atom ring expansion of methoxyl allenyl compounds 79 to prepare compounds 80 that can serve as precursors to isoquinolones was reported <02OL455,02SL480>. 

In the classical process a phenylethylamine reacts with a carboxylic acid chloride or anhydride to form an amide, which can be cyclised, with loss of water, to a 3,4-dihydroisoquinoline, then readily dehydrogenated to the isoquinoline using palladium, sulfur, or diphenyl disulfide. Common cyclisation agents are phosphorus pentoxide (P Ojq), phosphorus oxychloride and phosphorus pen-tachloride. The electrophilic intermediate is very probably an imino chloride, or phosphate the former have been isolated and treated with Lewis acids when they are converted into isonitrilium salts, which cyclise efficiently to 3,4-dihy-droisoquinolines. ... 

This concept was proven to be viable using the example of 4-nitrophenyl esters in the presence of a palladium(II) chloride/lithium chloride/isoquinoline catalyst system, the 4-nitrophenyl esters 3c of various aromatic, heteroaromatic and vinylic carboxylic acids were converted to the corresponding vinyl arenes 5k along with 4-nitrophenol (Figure 4.17). The latter was demonstrated to react with benzoic acid at the same temperature as required for the vinylation step (160 °C) to regenerate the corresponding ester [28], thus demonstrating that at least a two-step waste-minimized Mizoroki-Heck reaction is feasible. 

Treatment of o-ethynylbenzamides with a catalytic amount of PhCH2PdCl(PPh3)2 in THF at reflux results in 6-endo-dig cycUzation to give isoquinolin-l-ones (Scheme 2 )P Intercepting the o--vinylpalladium(II) intermediate derived from lV-carbomethoxy-2-alkynylaniline shown in Scheme 22 by allyl chloride produces 2-alkyl-3-allylindolesP This result proves involvement of the rr-bonded palladium(II) species. 

Isoquinolinylpalladium(II) intermediates of type 27 (Scheme 19.7) are useful precursors of 4-substituted isoquinolines. For example, when the reaction was carried out under a CO atmosphere in the presence of R X (aryl iodides/acyl chlorides) [8] or ROH [9], the corresponding ketones 29 or esters 31 were produced through carbony-lation (Scheme 19.8). Additionally, palladium(II)-catalyzed isoquinoline formation followed by a Heck reaction under oxidative conditions (CUCI2/O2) effectively produces 4-alkenylisoquinolines 33 [10]. 

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