Total Synthesis of Dixiamycins A and B via a Late-Stage N-N Bond Formation under Visible Light Photoredox Catalysis.

Intermolecular oxidative N-N bond formation reactions are quite challenging and are largely uncharted. N-N linked dimeric indolosesquiterpene alkaloids represent an underexplored class of natural products, and strategies for direct dehydrogenative N-N bond formation are limited. Here, we have reported that a late-stage visible-light photoredox catalysis facilitates N-N bond formation, leading to the total syntheses of atropo-diastereomers dixiamycins A () and B ().

Total Synthesis of (+)-7,7'-Bistaxodione via Late-Stage Electrochemical Dimerization.

The first asymmetric total synthesis of the tetraterpenoid (+)-7,7'-bistaxodione () via a unique late-stage electrochemical oxidative dimerization of a diterpenoid quinone methide tumor Inhibitor (+)-taxodione () has been described. The naturally occurring monomer was synthesized from aromatic abietane diterpenoid, ferruginol (1e) . Further, an efficient convergent synthetic route toward the naturally occurring aromatic abietane terpenoids has been shown via a Lewis acid-mediated diastereoselective cationic epoxy-ene cyclization.

Synthetic Approaches to Dimeric and Oligomeric Hexahydropyrrolo[2,3-b]indole Alkaloids.

Natural product synthesis has been the prime focus for the development of new chemical transformations and the drug discovery. The dimeric and oligomeric hexahydropyrrolo[2,3-b]indole alkaloids represent a architecturally intriguing class of cyclotryptamine alkaloids. These alkaloids share contiguous stereogenic centers with vicinal all-carbon quaternary stereogenic centers.

Total Synthesis of (+)- and (-)-Calycanthidine and Formal Synthesis of (-)-Idiospermuline via Key Pd(0)-Catalyzed Asymmetric Allylations.

We envisioned a novel asymmetric strategy to access unsymmetrically substituted dimeric 2-oxindoles [(,)- and (,)-] for the total synthesis of calycanthidine (). The key to success is the development of efficient Pd(0)-catalyzed asymmetric sequential allylations [via a highly enantioselective [up to 94% enantiomeric excess (ee)] and diastereoselective (up to ∼13:1) process] of unsymmetrically protected dimeric 2-oxindoles at the 3,3' position [such as (,)- and (,)-]. Gratifyingly, a mixture of bis-ester (±)-, ester-carbonates (±)- and (±)-, and bis-carbonate could afford (,)- and (,)- in highly stereoselective fashion, thereby culminating in the total synthesis of (+)-calycanthidine [-()] and (-)-calycanthidine ().

Asymmetric Synthesis of Taiwaniaquinone H via a Late-Stage Oxidative Decarboxylation.

The asymmetric syntheses of naturally occurring biologically relevant -abietane diterpenoids, (-)-taiwaniaquinone G (), and H () have been reported via a chiral pool strategy starting from commercially available abietic acid. A ring contraction of the middle ring of the [6,6,6]-carbotricyclic abietane diterpenoid core was carried out under the Wolff rearrangement. Finally, the synthesis of (-)-taiwaniaquinone H () was completed via a one-pot CAN-mediated oxidative decarboxylation.