THIQs nitroalkanes

Using a similar methodology, the group of C.-J. Li succeeded in performing a CDC reaction between tertiaiy amines and nitroalkanes where an ojq gen atmosphere was used as the oxidant. Interestingly, the catalyst used was magnetically recoverable Fe304 nanoparticles (10 mol%). Under such conditions, 1,2,3,4-tetrahydroisoquinoline (THIQ) compounds were... 

Liang performed the PIDA-induced sp C-H bond functionalization of tetrahydroisoquinolines (THIQs) (58) with nitroalkanes or malonates as the nucleophile (Scheme 8.21). The reactions involve the oxidation of 58 to an iminium intermediate (60) and nucleophilic attack to furnish the coupling products 59 and 60. 

Scheme 8.21 PIDA-Mediated cross-coupling of THIQs with nitroalkanes and malonates.

Using a catalytic amount of I2 in the presence of H2O2, CDC reaction of THIQs was achieved by Itoh (Scheme 8.49). Nitroalkane, ketone, and dimethyl malonate can be introduced to produce 100 in good yields. The generation of HOI from the oxidation of I2 or HI by H2O2 is expected to play an important role in the formation of the iminium ion intermediate 101, which reacts with the nucleophiles. 

A representative mechanism for the oxidative nitro-Mannich reaction of THIQs is shown in Scheme 10.5. Oxidation of the THIQ with excited state Ir gives the amine radical cation (la) and Ir. Catalyst turnover is presumed to occur by Ir -mediated reduction of either adventitious 0 q gen or the nitroalkane to the corresponding radical anion species. This radical anion can abstract the a-H atom of the amine radical cation, resulting in the formation of the iminium ion (Ila), which is then trapped by the nitroalkane. Alternatively, deprotonation of la can occur to form a-amino radical nia, which is then oxidized to form Ila. Stephenson and co-workers were able to rule out the role of singlet ojqrgen in the predominate reaction pathway by demonstrating that photosensitizers were ineffective in promoting this transformation. 

Figure 10.3). °" The aim of this approach is to minimize wasteful disposal of expensive rare earth metal complexes by instead utilizing recoverable photocatalysts that could be recycled in subsequent reactions without loss of activity. Lin and co-workers developed solid-supported photocatalysts by embedding chromophores into cross-linked polymers. The authors converted Ru(bpy)3 - and Ir(ppy)2(bpy) -based complexes into polymers by linking each chromophore with substituted tetraphenylmethane units to generate both porous and non-porous cross-linked polymers (PCP and CP, respectively) that are photochemically active. Using 0.2 to 1 mol% of Ru-PCP and Ir-PCP, nitro-Mannich reactions of THIQs were accomplished in the presence of nitroalkane solvents, air, and a 26 W CFL (Scheme 10.16). ... 

In addition to RB, eosin Y could be used for similar transformations of amines. Konig et al. utilized eosin Y and green LEDs to oxidize THIQ derivatives. The transient iminium ion was then trapped with a variety of nucleophiles including nitroalkanes, malonates, and diall lphosphonates (Scheme 10.31)." The addition of malonitrile, however, led to a-cyanation rather than formation of the (3-malonitrile, a result which has also been observed under non-photochemical oxidative conditions. ... 

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