First total syntheses of (±)-3-aza-11-selena and (±)-3-aza-11-tellura steroids

An efficient synthesis of 11-selena and 11-tellura steroids bearing a pyridine as an A ring was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes, which were generated from a 3-azabicyclo[4.2.0]octa-1,3,5-trien-7-one ketal. The major isomer matches the trans-anti-trans ring configuration of natural products. Finally, the vinyl groups of the synthesized 11-hetero steroids have been oxidized by the Wacker process in good yields. The characteristic ¹H and ¹³C NMR spectroscopic features of the synthesized compounds are reported.     

First total synthesis of 11-selena steroids

The first total synthesis of 11-selena steroids was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes as the key step.     

First total synthesis of 11-tellura steroids

The first total synthesis of 11-tellura steroids was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes as the key step.     

Efficient synthesis of new 11-thiasteroids and their oxides and dioxides

We show that our strategy, involving the use of an intramolecular Diels-Alder cycloaddition of o-xylylenes as the key step, can be applied efficiently to sulphur molecules. The synthesis of sulfoxide and sulfone derivatives is described and the vinyl group of those latters is oxidized, using the Wacker process, in good yields. Moreover, X-ray crystal structures of thiasteroids 11a and 12a matching the trans-anti-trans ring configuration of natural products are reported.     

A total synthesis of 11-O-methyldebenzoyltashironin

A concise total synthesis of 11-O-methyldebenzoyltashironin is reported in which oxidative dearomatization-IMDA-RCM triad constitutes the key ring forming steps, while an unorthodox DIBAL-H mediated stereo- and regioselective reductive epoxide openings and implementation of the vinyl bromide-carbonyl equivalency concept were pivotal to the success of this endeavor.     

Collective total synthesis of botryanes

The collective total synthesis of a series of botryanes, which are an important group of sesquiterpene antibiotics isolated from the metabolites of the fungus Botrytis cinerea, has been reported. The highly functionalized hydrindane skeleton of the botryanes was efficiently synthesized via an unusual intramolecular Diels-Alder reaction, which was promoted by TsOH as a protic acid. The concise total synthesis of (±)-hypocrolide A with a challenging hexacyclic skeleton was accomplished in 8 steps from the readily available starting materials.     

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.     

A new approach to the bicyclo[4.3.0] ring system of natural products from the liverwort: total synthesis of (±)-chiloscyphone and (±)-isochiloscyphone

Construction of the tricyclic derivative 5, a common intermediate for the synthesis of sesquiterpenoids 1-4, was accomplished by using the intramolecular Diels-Alder reaction. Availability of 5 was demonstrated by effective total synthesis of chiloscyphone 1 and isochiloscyphone 2.     

Neat total synthesis of six monoterpenic alkaloids of the actinidine series

A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[c]pyridine skeleton, (+)-deoxyrhexifoline (4), (+)-boschniakinic acid (5), (+)-boschniakine (6), (−)-plantagonine (7), (−)-indicaine (8) and (−)-tecostidine (9) is reported starting with the chiral precursor 3-bromo-5-((4R)-phenyloxazolin-2-yl)pyridine (10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5-exo-trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3R)- and (3S)-7-((4R)-phenyloxazolin-2-yl)cyclopenta[c]pyridines was separated by HPLC before being transformed into enantiopure natural products (4-9) by modification of the oxazoline group.     

Intramolecular Diels-Alder Reactions via 3-(Phenylthio)-4-(Trimethylsilyl)-3-Sulfolene

Deprotonation of the title compound 2 followed by treatment with 5-iodo-1-pentene or 6-iodo-l-hexene gave the alkylated products 3 and 4 which upon refluxing in toluene yielded the dienes 8a and 8b. Intramolecular Diels-Alder reactions were achieved by heating the dienes 8a and 8b in toluene in a sealed tube at 160–180°C to give bicyclo[4.3.0]nonene 9 and bicyclo[4.4.0]decene 10, respectively, in good yield. The stereochemistry of the cyclization products was determined, and was rationalized by comparison of the possible transition states involved.     

Progress towards the total synthesis of 2,3-dihydroxytrinervitanes

Intramolecular Diels-Alder approach to construct the fused AB ring of trinervitane has been demonstrated efficiently. The key intermediate for the Diels-Alder cyclization has been achieved following highly stereoselective Julia-Kocienski olefination, Sharpless epoxidation and Evan’s asymmetric alkylation as the key reactions.     

First regiospecific, enantiospecific total synthesis of gardnerine and gardnutine

The first enantiospecific total synthesis of gardnerine and gardnutine has been achieved from 6-methoxy-d-tryptophan via the asymmetric Pictet-Spengler reaction, a stereocontrolled intramolecular enolate driven palladium-mediated cross-coupling reaction and a chemospecific, regiospecific hydroboration/oxidation sequence as key steps.     

Angular hydroxymethyl directed intramolecular Diels-Alder approach for the stereo- and regioselective synthesis of pimaraditerpenes

The stereo- and regioselective synthetic route to pimaraditerpenes, employing an angular hydroxymethyl directed intramolecular Diels-Alder reaction of the decaline intermediate, has been developed. This synthetic approach allows prompt access to both natural pimaraditerpenes and the unnatural regioisomers, which would be potentially new anti-inflammatory pimaraditerpenes.     

A stereoselective total synthesis of (±)-tormesol

A general strategy for the synthesis of both trans/syn- and trans/anti-sphenolobane diterpenes has been developed, which utilizes an intramolecular ester enolate alkylation (IEEA) as a key step. A stereoselective total synthesis of (±)-tormesol (1), an unusual trans/syn-sphenolobane diterpene, was accomplished in 18 steps in 4.1% overall yield from readily available aldehyde 16.     

A stereoselective total synthesis of (−)-seychellene

A stereoselective total synthesis of the tricyclic sesquiterpene (−)-seychellene, starting from (R)-carvone via (R)-3-methylcarvone has been accomplished, employing a combination of intermolecular Michael addition-intramolecular Michael addition sequence, a stereoselective hydrogenation, and an intramolecular alkylation reaction.     

Domino pericyclic reactions of acyclic conjugated (E,Z,E,E)-tetraenes

Acyclic conjugated (E,Z,E,E)-tetraenes, upon thermolysis, undergo a domino pericyclic process involving 6π electrocyclisation of the (E,Z,E)-triene moiety to give the corresponding cis-disubstituted 5-vinyl-1,3-cyclohexadienes, followed by an intramolecular Diels-Alder reaction with the vinyl side chain to give tricyclo[3.2.1.0^2,7]oct-3-enes.     

Strategic innovations for the synthesis of vinigrol

Since the isolation of unique tricyclic diterpenoid vinigrol, its promising biological activities and complex framework have resulted in numerous synthetic efforts to the total synthesis of this venerable molecule for the past two and half decades. This mini review highlights the significance of various synthetic strategies towards this structurally unique and challenging natural product.     

Towards the total synthesis of tangutorine by intramolecular Diels-Alder reaction

The syntheses of 3,5-disubstituted-2-sulfolenes, and their participation in Pictet-Spengler reactions to give precursors of tangutorine, are described.     

Intramolecular Heck cyclization to the galanthamine-type alkaloids: total synthesis of (±)-lycoramine

A novel approach towards the construction of the galanthamine skeleton was demonstrated by the total synthesis of (±)-lycoramine. The key steps include a Pd-catalyzed intramolecular cyclization to form the seven-membered azepane ring and a spontaneous intramolecular Michael addition to afford the five-membered furan ring. This synthetic route has also been demonstrated to be useful for the preparation of novel derivatives with simplified galanthamine skeletons.     

Towards the total synthesis of tashironin related allo-cedrane natural products: further exploitation of the oxidative dearomatization-IMDA-RCM triad based strategy

Synthetic studies directed towards allo-cedrane based, tashironin sibling natural products, involving some deft functional group manipulations on a preformed tetracyclic scaffold, are delineated.