Journal
SYNLETT
Volume 30, Issue 15, Pages 1825-1829Publisher
GEORG THIEME VERLAG KG
DOI: 10.1055/s-0039-1690006
Keywords
catalysis; cyclization; electron transfer; iridium; photochemistry; radical reaction
Categories
Funding
- Deutsche Forschungsgemeinschaft (DFG)
- TUM graduate school
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Starting from the respective tertiary alpha-silylmethyl amines, the intramolecular cyclization of alpha-aminoalkyl radicals to Michael acceptors produced tetrahydroisoquinolines. The reaction conditions included the use of 5 mol% of an iridium photoredox catalyst, dimethylformamide as the solvent, and equimolar amounts of water and cesium carbonate as the additives. 13 substrates were synthesized from ortho-alkylbenzaldehydes in a three-step procedure involving a carbonyl condensation, a radical bromination, and a substitution by a secondary alpha-silylmethyl amine. After optimization of the photocyclization, the reaction delivered tetrahydroisoquinolines in moderate to high yields (41-83%). A facial diastereoselectivity (dr congruent to 80:20) was observed with chiral substrates and a crystal structure provided evidence for the relative configuration of the major diastereoisomer. A catalytic cycle with direct electron transfer to the photoexcited metal catalyst is proposed.
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