The use of photoredox catalyst [Au2(dppm)2]Cl2 to initiate free-radical cyclizations onto indoles is reported. Excitation of the dimeric Au(I) photocatalyst for the reduction of unactivated bromoalkanes and bromoarenes is used for the generation of carbon-centered radicals. Previous to this work, reduction processes leading to indole functionalization utilizing photoredox catalysts were limited to activated benzylic or α-carbonyl-positioned bromoalkanes. This method offers a mild and safe alternative to organostannanes and pyrophoric initiators for access to high energy radicals that were previously inaccessible through catalytic or stoichiometric means.
Two tandems are faster than one! Properly sequenced reactions initiated by the Petasis aminoalcohol synthesis from boronic acids, diallylamine, and α‐hydroxyaldehydes, including free aldoses, leads to rapid construction of complex enantiopure structures (see scheme).
The three-component Petasis borono-Mannich reaction starting with easily accessible N-protected α-amino aldehydes produces efficiently and diastereoselectively 1,2-trans-diamines with an enantiomeric excess of up to 98%.
An unprecedented intramolecular Petasis condensation provides a novel approach to biologically important conduramines. The compounds are produced with an exclusive anti stereoselectivity for the newly created β-amino alcohol motif. The stereochemical outcome of the reaction is opposite to the one usually observed in the intermolecular reaction.
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