Rhodium-catalyzed synthesis isoquinolines

Similarly, ketimines (benzylimines of aromatic ketones) undergo the rhodium-catalyzed ortho-alkenylation with alkynes to give or/ o-alkenylated aromatic ketones after hydrolysis.61 This method is applied to an efficient one-pot synthesis of isoquinoline derivatives by using aromatic ketones, benzylamine, and alkynes under Rh catalysis (Equation (55)). 

A rhodium-catalyzed one-pot synthesis of substituted pyridine derivatives from a,(3-unsaturated ketoximes and alkynes was developed in 2008 by Cheng and coworkers [99], Good yields of the desired pyri-dines can be obtained (Scheme 3.48). The reaction was proposed to proceed via rhodium-catalyzed chelation-assisted activation of the (3—C—H bond of a,(3-unsaturated ketoximes and subsequent reaction with alkynes followed by reductive elimination, intramolecular electro-cyclization, and aromatization to give highly substituted pyridine derivatives finally [100]. Later on, in their further studies, substituted isoquinolines and tetrahydroquinoline derivatives can be prepared by this catalyst system as well [101]. Their reaction mechanism was supported by isolation of the ort/jo-alkenylation products. Here, only asymmetric internal alkynes can be applied. 

Guimond N, Fagnou K (2009) Isoquinoline synthesis via rhodium-catalyzed oxidative cross-coupling/cyclization of aryl aldimines and alkynes. J Am Chem Soc 131 12050-12051 Booth BL, CoUis A (1989) One-step synthesis of A -(l-benzylisoquinohn-3-yl)phenylacet-amidinium trifluoromethanesulphonate derivatives from phenylacetonitiiles and trifluoro-methanesulphonic Acid. J Chem Res Synop 304-305... 

The enantioselective synthesis of axially chiral P—N ligands was also accomplished by rhodium-catalyzed [2 + 2+-2] cycloaddition. The reactions of 1,6-diynes 75 with diphenylphosphinoyl-substituted isoquinolinyl acetylenes 76 furnished diphenylphosphinoyl-substituted axially chiral 1-arylisoquinolines 77 with high yields and ee values (Scheme 9.28) [23], The new diphenylphosphinoyl-substituted axially chiral 1-arylisoquinoline 77 (Z = NTs, R = Me) was derivatized to the corresponding axially chiral P—N ligand 78 and isoquinoline A-oxide 79 without racemization, which could be used in the rhodium-catalyzed hydroboration and Lewis base-catalyzed allylation, respectively [23],... 

In 2012, Cheng and coworkers reported a one-pot synthesis of isoquinolinium salts by rhodium-catalyzed C-H alkenylation/annulation reactions [73] and applied it to the synthesis of oxychelerythrine, an isoquinoline alkaloid (Scheme 16.36) [74]. The reaction of aldehyde 164 with alkyne 165 in the presence of... 

R =aryl) in aprotic solvents, for example, xylene at 140 °C, is more important and has been applied very frequently to prepare indoles of type 176 via intermediate 172. This method is connected with the names of Hemetsberger and Knittel and can be transferred to the synthesis of azaindoles, fused indoles, and fused pyrrol derivatives. Quite recently, reactions like 171 (R =Ph) —> 176 have been conducted in a rhodium(II)-catalyzed way, which allows to decrease the necessary temperature into a range of 25-60 C. The transformation of 171 into isoquinolines is also possible if one or both ortho positions of the aryl group R are substituted appropriately. ... 

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