Concise approach to the syntheses of (±)-gliocladin C and related diketopiperazine alkaloids

A unique approach to the diketopiperazine indole alkaloid (±)-gliocladin C was developed and applied to formal syntheses of the related alkaloids (±)-gliocladine C and (±)-T988C. The key features of the strategy include an unprecedented nucleophilic addition of a diketopiperazine to an isatin derivative followed by a Friedel-Crafts alkylation of the resultant tertiary alcohol with indole to establish the critical quaternary center. Subsequent reduction of the intermediate oxindole moiety and cyclization then delivered a pivotal hexahydropyrrolo[2,3-b]indole diketopiperazine intermediate that was readily converted into (±)-gliocladin C as well as racemic versions of key intermediates in the Overman syntheses of (+)-gliocladine C and (+)-T988C.     

Total syntheses of (±)-securinine and (±)- allosecurinine

Total syntheses of (±)-securinine and (±)-allosecurinine that employ a tandem rhodium carbenoid-initiated Claisen/α-ketol rearrangement sequence as a key step are described.     

A highly diastereoselective total synthesis of (±)-heritonin and (±)-heritol

A highly diastereoselective synthesis of heritol and heritonin by intramolecular cyclization on a preformed sensitive butenolide functionality is described.     

Efficient generation of ortho-quinone methide: application to the biomimetic syntheses of (±)-schefflone and tocopherol trimers

An efficient method using silver oxide-mediated oxidation for the synthesis of ortho-quinone methides has been developed and applied to the biomimetic syntheses of novel trimeric natural products, (±)-schefflone and tocopherol trimers. Further studies of the critical trimerization as well as substrate scope and limitations are also reported.     

Concise and protective group-free syntheses of (±)-hamigeran B and (±)-4-bromohamigeran B

Concise and protective group free syntheses of (±)-hamigeran B and (±)-4-bromohamigeran B are reported. The key reactions include an enone migration and a Diels-Alder cyclization to provide the requisite tricyclic skeleton.     

An Expedient Approach to the Benzopyran Core: Application to Synthesis of the Natural Products(±)-Xyloketals and(±)-Alboatrin

A mild and efficient protocol for the synthesis of the benzopyran ring has been described and a series of chromans compounds is reported, the yield is from 72% to 95%. The diadduct tended to angular product and showed good regioselectivity. This strategy was applied for the benzopyran derived natural products (±)‐xyloketals and (±)‐alboatrin. The crystal of compound 9 exhibited centro‐symmetric space group, containing two isomers in one unit. The relative configurations were 1R,10R,15S and 34S,22R,30S, respectively.     

Unified approach to the sesquiterpenoids,lauranes and cyclolauranes: Total synthesis of (±)-isolaurene

A general approach to the total synthesis of sesquiterpene, isolaurene (1a) and cyclolaurene (2a) is featured from commercially available 3-methyl cyclopenten-2-one. The strategy includes a Stork-Danheiser sequence concomitant with a Ni(II)-catalyzed conjugate addition of methyl group onto 3-aryl 2-methyl cyclopenten-2-one to afford the advanced intermediate 11. A methyllithium addition onto compound 11 with an eventual dehydration completed the total synthesis of isolaurene (1a) in 5 steps (58.3% overall yields).     

Controlled functionalization of cyclohepta-l,3-diene: An approach to the (±) prelog-djerassi lactonic acid.

The cycloheptenone (1c), a precursor to the (±) Prelog - Djerassi lactonic acid (2), has been synthesized stereoselectively from cyclohepta-l,3-diene.     

Scalable, stereocontrolled total syntheses of (±)-axinellamines A and B

The development of a simple, efficient, scalable, and stereocontrolled synthesis of a common intermediate en route to the axinellamines, massadines, and palau'amine is reported. This completely new route was utilized to prepare the axinellamines on a gram scale. In a more general sense, three distinct and enabling methodological advances were made during these studies: (1) an ethylene glycol-assisted Pauson-Khand cycloaddition reaction, (2) a Zn/In-mediated Barbier-type reaction, and (3) a TfNH(2)-assisted chlorination-spirocyclization.     

Oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade for the syntheses of (±)-atisine and (±)-isoazitine

A convergent and efficient formal synthesis of (±)-atisine has been accomplished. The synthetic strategy is to efficiently construct the bicyclo[2.2.2]octane ring moiety by an oxidative dearomatization/intramolecular Diels-Alder cycloaddition cascade. The first total synthesis of another atisine-type C(20)-diterpenoid alkaloid, (±)-isoazitine, has also been achieved employing the same strategy.     

Novel approach to the synthesis of aliphatic and aromatic α-keto acids

A new practical and efficient synthesis of α-keto acids was accomplished starting from the synthon 1,4-diacetylpiperazine-2,5-dione. The synthesis encompasses both aromatic and aliphatic substrates proving to be versatile and innovative with excellent carbon economy and recycling of the glycine by-product.     

Photochemical Synthesis of Aporphines: (±)-Glaucine, (±)-Norglaucine and (±)-Dehydronorglaucine

Photochemical cyclization of 3 afforded 5, 4 and 8.5 on LAH reduction furnished (±)-glaucine (6) and on treatment with ethanolic HCl afforded (±)-norglaucine (7). 10 obtained by the photocyclization of 9 was converted into 7 and 11 via 12.     

Fast and protecting-group-free synthesis of (±)-subincanadine C

The first total synthesis of (±)-subincanadine C has been accomplished in a protecting-group-free fashion. This pentacyclic indole alkaloid was synthesized in six steps from the known intermediate 4, featuring Ni(COD)(2)-mediated intramolecular Michael addition as a key transformation.     

Total synthesis of (±)-pallambins C and D

The first total synthesis of (±)-pallambins C and D has been accomplished in a linear 38 step reaction from (±)-Wieland-Miescher ketone. The key conversions are featured as follows: a Grob fragmentation-intramolecular aldol cyclization and a thiourea/palladium-catalyzed carbonylative annulation.     

An alternative Route to (±)-Warburganal Synthon

The transformation of the ketone (1) to the unsaturated diester (11) a potential intermediate for the warburganal (12) is described. The Wittig reaction of theketone (1) with methylenetriphenylphosphorane afforded the olefin (2) which reacts with Woodward's reagent (MeCOOAg, I₂ and MeCOOH and H₂O) to give the diol (13). This on heating with dimethylsulfoxide afforded the tetralin (14)