First total synthesis of (−)-diospongin B

The first total synthesis of (−)-diospongin B has been achieved starting from benzaldehyde using chiral allylation, a base catalyzed conjugate addition of an α,β-unsaturated ester and an intramolecular oxy-Michael reaction as the key steps in 16% overall yield.     

Organocatalytic asymmetric Michael addition of 2,4-pentandione to nitroolefins

[reaction: see text] A novel binaphthyl-derived amine thiourea organocatalyst has been developed and demonstrated to efficiently catalyze Michael addition reactions (using as low as 1 mol % loading) of diketones to nitroalkenes with remarkably high enantioselectivities.     

First enantioselective total synthesis of (−)-heliannuol C

The first, efficient total synthesis of (−)-heliannuol C (1) was accomplished enantioselectively, using a chemoenzymatic desymmetrization of the σ-symmetrical diol, a ring closing metathesis, a diastereoselective epoxidation, and a regioselective reductive cleavage of epoxide as the key reaction steps.     

Organocatalytic asymmetric direct Michael addition of aromatic ketones to alkylidenemalononitriles

The asymmetric direct Michael addition of aromatic ketones to highly active alkylidenemalononitriles was investigated by employing a chiral primary amine 9-amino-9-deoxyepicinchonine. In general modest to good enantioselectivities (71–84% ee) could be obtained in acceptable isolated yields (48–85%) for an array of substrates.     

Efficient, asymmetric synthesis of (−)-isooncinotine

Asymmetric synthesis of (−)-isooncinotine, a 22-membered lactam of spermidine alkaloid, starting from resolution of 2-piperidineethanol with (S)-10-camphorsulfonic acid is reported. Michael addition, amidations, and aluminum hydride reduction were applied to form the moiety of spermidine. Retro-Michael addition was observed when β-amido- and β-amino-propionitriles were reduced by LAH. The effects of LAH versus AlH₃ were discussed. The synthesis of the skeleton of this macrolide is achieved with ring-closing metathesis of the diene prepared from acylation of the spermidine.     

First total synthesis of neurotrophic diacetylene tetrol (−)-petrosiol D

The first total synthesis of the natural product (−)-petrosiol D has been achieved in a linear fashion. Sharpless asymmetric epoxidation, base induced elimination reaction for the formation of chiral propargyl alcohol and Cadiot–Chodkiewicz coupling reaction are the key steps utilized for the synthesis.     

Concise asymmetric synthesis of (−)-herbertenediol

The rearrangement of the optically active 3-aryl-2-methyl-2,3-epoxy tosylate (>98% ee) afforded the α-keto tosylate with a chiral quaternary carbon center and without loss of chirality. Reductive removal of the tosyloxy group gave the keto compound with a chiral quaternary carbon center, which was converted to (−)-herbertenediol (>98% ee).     

First total synthesis of (±)-epocarbazolin A and epocarbazolin B, and asymmetric synthesis of (−)-epocarbazolin A via Shi epoxidation

Epoxidation of the trisilyl-protected carbazomadurins A and B with dimethyldioxirane followed by desilylation provides a simple route to racemic epocarbazolin A and a non-diastereoselective access to epocarbazolin B. The Shi epoxidation has been applied to an asymmetric synthesis of the non-natural (−)-epocarbazolin A.     

Organocatalytic asymmetric total synthesis of (R)-rolipram and formal synthesis of (3S,4R)-paroxetine

An efficient enantioselective total synthesis of (R)-rolipram and an efficient enantioselective formal synthesis of (3S,4R)-paroxetine has been achieved using the highly enantioselective Michael addition of malonate nucleophiles as key steps in both cases.     

Organocatalytic and direct asymmetric vinylogous Michael addition of alpha,alpha-dicyanoolefins to alpha,beta-unsaturated aldehydes

The first highly regio-, chemo-, diastereo- and enantioselective direct vinylogous Michael addition of alpha,alpha-dicyanoolefins to alpha,beta-unsaturated aldehydes is described, employing readily available chiral alpha,alpha-diarylprolinol salts as iminium organocatalysts.     

Stereoflexible total synthesis of (−)-epiquinamide

Hydroxy propiolate rearrangement to conjugated diene, Sharpless asymmetric dihydroxylation and one-pot quinolizine construction have been used as key steps in the total synthesis of (−)-epiquinamide.     

Stereocontrolled total synthesis of (−)-aspidophytine

The enantioselective stereocontrolled total synthesis of aspidophytine is described. The key indole intermediate was prepared by radical cyclization of 2-alkenylphenylisocyanide, followed by Sonogashira-coupling with a highly functionalized terminal acetylene. The 11-membered cyclic amine, a precursor for the formation of the aspidosperma skeleton, was synthesized using nitrobenzenesulfonamide chemistry. After construction of the pentacyclic skeleton, the lactone ring was formed to complete the total synthesis.     

Enantioselective total synthesis of (−)-pseudophrynaminol through tandem olefination, isomerization and asymmetric Claisen rearrangement

A new and efficient total synthesis of (−)-pseudophrynaminol, the pyrrolo[2,3-b]indole alkaloid bearing the allylic moiety at the 3a-position, has been achieved by a sequence involving 3-allylindol-2-one 8 as a key intermediate. The enantioselective construction of the quaternary carbon in 8 was performed through a tandem cascade reaction of 2-allyloxyindolin-3-one 4, olefination, isomerization, and asymmetric Claisen rearrangement.     

Second-generation total synthesis of (−)-diversifolin

A second-generation total synthesis of (−)-diversifolin has been achieved by a more straightforward strategy, involving a highly stereochemistry-dependent 10-membered ring-closing metathesis and a stereoselective dihydroxylation/lactone transposition sequence. Compared to our previous synthesis, the present synthesis is improved in the yield of the key intermediate 2 (20% in 12 steps from diol 8).     

Stereoselective total synthesis of (−)-pyrenophorol

An efficient stereoselective total synthesis of (−)-pyrenophorol 1 is described. The key steps involved in this synthesis are hydrolytic kinetic resolution (HKR), MacMillan α-hydroxylation, Horner-Wadsworth-Emmons (HWE) reaction, and Mitsunobu cyclization.     

Formal total synthesis of (−)-spongidepsin

The formal total synthesis of (−)-spongidepsin is described. Three fragments I, II, and III were first prepared from readily available starting materials and then assembled to the target compound. The key steps involved in the synthesis are asymmetric α-hydroxylation, Ender's alkylation, and ring-closing metathesis reactions. An alternative route for the fragment II is also achieved involving Sharpless asymmetric epoxidation and Gilman's alkylation as key reactions.     

The total synthesis of (−)-tetrahydrolipstatin

Careful control during the bromolactonisation of β,γ-unsaturated acid 3 was required to afford regioselectively the trans-β-lactone 4 as the major diastereomer. Radical debromination of 4 followed by a three-step sequence of reactions afforded the lipase inhibitor (−)-tetrahydrolipstatin.     

Enantioselective total synthesis of (−)-microcarpalide

The enantioselective total synthesis of the actin-targeting metabolite (−)-microcarpalide is described. Key steps include ring-closing metathesis (RCM) for the final construction of the 10-membered lactone framework and stereoselective homologation of boronic esters for the insertion of all stereocentres with the desired absolute configuration. In particular, the acidic fragment was prepared in seven steps from a suitable chiral bromomethane boronate by means of two sequential stereoselective homologations to install the two stereocentres with the correct final R stereochemistry, employing (−)-pinanediol as the chiral director. Subsequent elaboration to the required C₇ backbone entailed nucleophilic displacement with a vinyl Grignard reagent, oxidative cleavage of the boronic scaffold and protection-deprotection manipulations. Interestingly, when the tribenzyloxy diene ester resulting from DCC-mediated coupling of the two key synthons was subjected to RCM in the presence of Grubbs' catalyst, the reaction proceeded stereoselectively to yield the desired trans oxecin-2-one, albeit with poor conversion.     

Stereoselective total synthesis of (−)-brevisamide

The stereoselective total synthesis of (−)-brevisamide, a novel marine cyclic ether alkaloid isolated from dinoflagellate karenia brevis is described. The key steps involved in this synthesis are the Sharpless asymmetric epoxidation and regioselective ring opening of chiral epoxide by Gilman's reagent. The tetrahydropyran core has been constructed by an intramolecular S_N2 cyclisation.