Peter Bellotti

The nonequilibrium triplet state of molecules plays an important role in photocatalysis, organic photovoltaics, and photodynamic therapy. We report the direct measurement of the triplet lifetime of an individual pentacene molecule on an insulating surface with atomic resolution by introducing an electronic pump-probe method in atomic force microscopy. Strong quenching of the triplet lifetime is observed if oxygen molecules are coadsorbed in close proximity. By means of single-molecule manipulation techniques, different arrangements with oxygen molecules were created and characterized with atomic precision, allowing for the direct correlation of molecular arrangements with the lifetime of the quenched triplet. Such electrical addressing of long-lived triplets of single molecules, combined with atomic-scale manipulation, offers previously unexplored routes to control and study local spin-spin interactions.

Herein, the radical three‐component carbonyl propargylation between 1,3‐enynes, aldehydes, and suitable radical precursors through dual chromium/photoredox catalysis is reported for the first time. This redox‐neutral reaction occurs under very mild conditions, shows high functional group tolerance and represents a complementary novel approach for preparing valuable synthetic architectures from simple chemicals.

Abstract

Carbonyl propargylation has been established as a valuable tool in the realm of carbon–carbon bond forming reactions. The 1,3‐enyne moiety has been recognized as an alternative pronucleophile in the above transformation through an ionic mechanism. Herein, we report for the first time, the radical carbonyl propargylation through dual chromium/photoredox catalysis. A library of valuable homopropargylic alcohols bearing all‐carbon quaternary centers could be obtained by a catalytic radical three‐component coupling of 1,3‐enynes, aldehydes and suitable radical precursors (41 examples). This redox‐neutral multi‐component reaction occurs under very mild conditions and shows high functional group tolerance. Remarkably, bench‐stable, non‐toxic, and inexpensive CrCl₃ could be employed as a chromium source. Preliminary mechanistic investigations suggest a radical‐polar crossover mechanism, which offers a complementary and novel approach towards the preparation of valuable synthetic architectures from simple chemicals.

Enantioselective syntheses of strychnos and chelidonium alkaloids were achieved via the regio‐ and stereocontrolled synthesis of homoallylic amines through isothiourea/transition‐metal cooperative catalysis. Indole acetic acid esters were established as remarkably effective nucleophiles, enabling syntheses of akuammicine, strychnine, and an SIRT‐1 inhibitor. Structure‐based reactivity challenges were overcome to synthesize three chelidonium alkaloids.

Abstract

We describe enantioselective syntheses of strychnos and chelidonium alkaloids. In the first case, indole acetic acid esters were established as excellent partner nucleophiles for enantioselective cooperative isothiourea/Pd catalyzed α‐alkylation. This provides products containing indole‐bearing stereocenters in high yield and with excellent levels of enantioinduction in a manner that is notably independent of the N‐substituent. This led to concise syntheses of (−)‐akuammicine and (−)‐strychnine. In the second case, the poor performance of ortho‐substituted cinnamyl electrophiles in the enantioselective cooperative isothiourea/Ir catalyzed α‐alkylation was overcome by appropriate substituent choice, leading to enantioselective syntheses of (+)‐chelidonine, (+)‐norchelidonine, and (+)‐chelamine.

Shine on you crazy Pd! The dicarbofunctionalization of tri‐ and tetrasubstituted olefins to form (hetero)cyclic compounds under photoinduced palladium catalysis is described. A broad range of highly decorated olefins tethered to aryl or alkyl bromides were coupled with styrenes or acryl amides. One or two contiguous all‐carbon quaternary centers can be formed in a single step with this procedure.

Abstract

The redox‐neutral dicarbofunctionalization of tri‐ and tetrasubstituted olefins to form a variety of (hetero)cyclic compounds under photoinduced palladium catalysis is described. This cascade reaction process was used to couple styrenes or acryl amides with a broad range of highly decorated olefins tethered to aryl or alkyl bromides (>50 examples). This procedure enables one or two contiguous all‐carbon quaternary centers to be formed in a single step. The products could be readily diversified and applied in the synthesis of a bioactive oxindole analogue.