Chromoselective access to Z- or E- allylated amines and heterocycles by a photocatalytic allylation reaction

Abstract

The most useful strategies for the alkylation of allylic systems are related to the Tsuji–Trost reaction or the use of different Lewis acids. Herein we report a photocatalytic approach for the allylation reaction of a variety of nucleophiles, such as heteroarenes, amines and alcohols. This method is compatible with a large variety of pyrroles and indoles, containing different substituents such as electron-withdrawing and electron-donating groups, unprotected nitrogen atoms and bromo derivatives. Moreover, this methodology enables the chromoselective synthesis of Z - or E -allylated compounds. While the use of UV-light irradiation has allowed the synthesis of the previously inaccessible Z -allylated products, E -isomers are prepared simply by changing both the light source to the visible region, and the catalytic system. Based on mechanistic and photochemical proofs, laser flash photolysis studies and DFT calculations, a rational mechanism is presented.

Metal-free photoredox-catalysed formal C–H/C–H coupling of arenes enabled by interrupted Pummerer activation

“…Substrates bearing halogens, triflyl, mesyl, keto, amido, ester, trifluromethyl, and cyano groups all provided the desired heterobiaryls with complete chemoselectivity (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). The high chemoselectivity observed in the reduction of the Ar-DBT + group is particularly noteworthy, given that PTH has previously been shown to catalyse the reduction of aryl halides [45][46][47][48] and trifluoromethyl groups. 49 The process' tolerance of halide and triflyl functional groups signals its orthogonality with regard to traditional crosscoupling and ensures that further structural modification of products can be carried out using conventional cross- While thiophene substrates showed some compatibility (31)(32)(33), furan and pyrrole were too reactive (34,35).…”

“…We next evaluated the scope with respect to the trapping (hetero)arene. A range of substituted pyrroles (36)(37)(38)(39), thiophenes (40)(41)(42), furans (43)(44)(45)(46)(47), benzofuran (48), and indole (49) partners was used successfully in the coupling. In the cases of 3-substituted heterocycles, complete regiocontrol was observed (42, 46, and 47).…”

Chromoselective Synthesis of Sulfonyl Chlorides and Sulfonamides with Potassium Poly(heptazine imide) Photocatalyst

“…Considering the chromoselective catalysis by carbon nitrides and molecular catalysts[ 13a , 13b , 13c , 15 ] and the multiple reaction paths feasible for S‐phenylthioacetates[ 21 , 22 , 23 , 24 ] under redox conditions, we explored the impact of excitation wavelength on the selectivity of S‐arylthioacetates conversion. To this end, three substrates with different electronic properties were selected, that is, electron rich 4‐methoxyphenylthioacetate, electron deficient 2‐trifluoromethylphenylthioacetate, and bare phenylthioacetate.…”

Reactivity control of a photocatalytic system by changing the light intensity

“…14,15 In a somewhat related approach, a photocatalytic allylation was combined with a lightcolor selective isomerization to control product formation. 16 While these recent chromoselective methods 15,16 are very elegant and clearly have an impact on photoredox catalysis, they both rely on irradiation equipment consisting of at least two high-power LEDs as light sources.…”