An expedient synthesis of (±)-centrolobine

An expedient synthesis of the antibiotic natural product centrolobine is reported, the key step being the one pot, multi-component construction of a tetrahydropyran-4-one via a ‘revisited’ Maitland-Japp reaction.     

Total synthesis of (−)-centrolobine: β-C-glycoside formation via a tandem Grignard addition and stereoselective hemi-ketal reduction

It has been demonstrated that an aryl-β-C-glycoside can be efficiently constructed via a sequence consisting of Brown asymmetric allylation, ring-closing metathesis, hydrogenation, nucleophilic addition, and stereoselective Et₃SiH reduction. The antibiotic natural product (−)-centrolobine was synthesized in this manner utilizing only five steps with an overall 53% yield.     

One-pot total syntheses of natural products containing a THP-ring backbone: (±)-centrolobine and (±)-civet cat secretion

A one-pot strategy is devised and applied to the total syntheses of natural products with a THP-ring backbone. A special feature of this one-pot synthesis is the recyclability of the indium complex byproduct generated from the indium-mediated allylation reaction for concurrent catalysis in subsequent steps. Centrolobine and civet cat secretion are synthesized via this new method in overall yields of 58% and 23%, respectively.     

Two successive one-pot reactions leading to the expeditious synthesis of (−)-centrolobine

A very short and efficient synthesis of (−)-centrolobine has been achieved by using two successive one-pot reactions. The first sequence involves a cross-metathesis reaction/hydrogenation/lactonization and the second sequence is a Grignard addition/reduction.     

Suppression of epimerization due to selectivity leakage: an application towards the total synthesis of (−)-centrolobine

An InCl₃-mediated Prins cyclization of homoallylic alcohols with aldehydes has been established. The enantioselectivities of the trisubstituted tetrahydropyrans are almost retained through the suppression of epimerization. The synthetic value of this protocol is demonstrated by the total synthesis of (−)-centrolobine.     

Sequential pericyclic reaction of ene-diallene: synthesis of (±)-estrone

The one-pot construction of perhydrophenanthrene from an acyclic substrate was achieved via a sequential pericyclic reaction, which involved the in situ generation of ene-diallene species due to Myers' propargyl alcohol-allene transformation. The resulting perhydrophenanthrene derivative could be successfully converted into (±)-estrone.     

Total synthesis of (−)-centrolobine

Stereoselective synthesis of (−)-centrolobine, an anti-Leishmania agent, was accomplished via an intramolecular Barbier-type reaction of iodo-ester with n- or t-butyllithium followed by Lewis acid-promoted Et₃SiH reduction of the resulting hemiacetal.     

Total synthesis of (+/−)-diospongin A via Prins reaction

A straightforward synthesis of (+/−)-diospongin A starting from benzaldehyde is described. A Prins cyclization reaction to control the relative configuration of the three stereogenic centers and a Mitsunobu inversion represent the key steps of the approach.     

Asymmetric synthesis of the pyran antibiotic (−)-centrolobine

An expedient total synthesis of (−)-centrolobine is achieved involving asymmetric Keck allylation and stereoselective intramolecular oxy-Michael reactions as key steps in 8% overall yield.     

Stereoselective formal synthesis of (−)-centrolobine

Stereoselective formal synthesis of (−)-centrolobine was achieved from naturally occurring l-(+)-tartaric acid, employing a facile FeCl₃ mediated stereoselective formation of a tetrahydropyran as the key step.     

Synthesis of (±)-coerulescine and a formal synthesis of (±)-horsfiline

A straightforward synthesis of (±)-coerulescine and (±)-horsfiline has been established from 3-formyl-3-phenylpyrrolidine employing 4-hydroxypiperidine as the starting material. There are two remarkable steps for the synthesis of (±)-coerulescine and (±)-horsfiline. One is the rapid access to produce 3-formyl-3-phenylpyrrolidine by Lewis acid-catalyzed rearrangement of 3,4-dihydroxy-4-phenylpiperidine. The other key step is an intramolecular electrophilic cyclization from 3-benzylcarbamoyl-3-phenylpyrrolidine to the 3,3-spirocyclic 2-oxindole ring skeleton.     

Formal synthesis of (±)-brazilin and total synthesis of (±)-brazilane

A convergent synthesis towards (±)-brazilin and (±)-brazilane has been reported from 3,4-dimethoxy benzaldehyde in <15 reaction steps. Palladium(II)-catalysed intramolecular Friedel–Crafts cyclisation and Lewis acid supported intermolecular Friedel–Crafts alkylation reactions have been demonstrated. A tetracyclic substituted indane common key intermediate is employed to furnish the desired two molecules in good to excellent yield. Pd(OH)₂ has played a crucial role in the total synthesis of (±)-brazilane.     

Total synthesis of (±)-hyrtiazepine

The total synthesis of the azepinoindole alkaloid, (±)-hyrtiazepine, was achieved. Construction of the azepinoindole core structure was carried out by C-4 selective α-hydroxyalkylation of 5-hydroxyindole, introduction of serine at C-3 of the indole moiety, and intramolecular imination.     

Total synthesis of (±)-herbertenediol

A formal total synthesis of the sesquiterpene (±)-herbertenediol and its dimers mastigophorenes A-D has been accomplished, starting from vanillin via 2,3-dimethoxy-5-methylbenzaldehyde. A combination of Claisen rearrangement and ring-closing metathesis reactions were employed for the generation of the two vicinal quaternary carbons on a cyclopentane ring.     

Total synthesis of (±)-monomorine

An efficient, two-operation synthesis of the trail ant pheromone (±)-monomorine is reported. The synthesis features an aqueous Claisen-Schmidt condensation followed by the stereocontrolled installation of the three resident stereocenters in a single operation.     

Stereoselective synthesis of (±)-tacamonine

We report a stereocontrolled approach to the pentacyclic indole alkaloid tacamonine by modifying an earlier route using norbornadiene to supply the nontryptamine portion. By maintaining a bridged system the reduction step of the Bischler-Napieralski reaction proceeded to deliver a bridged diol in which three methine hydrogen atoms are in an all-cis configuration. All 19 skeletal carbon atoms are fully incorporated, therefore, the only remaining steps involved cleavage of the vic-diol subunit in the seven-membered ring and further oxidation and reduction of the resulting lactam aldehyde.     

Pd(0) catalyzed intramolecular Heck reaction: a versatile route for the synthesis of 2-aryl substituted 5-, 6-, and 7-membered O-containing heterocycles

An efficient and convenient method for the synthesis of 2-aryl substituted tetrahydropyran, tetrahydrofuran, and oxepine derivatives via intramolecular palladium catalyzed cyclization is developed. The two exo-cyclic double bonds at adjacent carbon atoms in these ring systems could serve as potential dienes for cycloaddition reactions.     

Total synthesis of (±)-antofine

An efficient preparation of (±)-antofine is described. The main steps involved in this synthesis are the Horner–Wadsworth–Emmons reaction, the intramolecular Schmidt reaction of an azido aldehyde, and the one-pot deprotection of the N-formyl group, followed by Pictet–Spengler cyclization. The asymmetric hydrogenation of the trisubstituted α,β-unsaturated ester is also explored, however only moderate enantio-control (55% ee) is obtained. Finally, (±)-antofine is prepared in six steps from the phenanthryl aldehyde 5 with an overall yield of 35%.     

Total synthesis of (±)-cyclooroidin

The first total synthesis of (±)-cyclooroidin, a member of the pyrrole-imidazole alkaloid family recently isolated from the sponge Agelas oroides in optically pure form, is described. The synthesis was achieved in nine linear steps, with an overall yield of 10%. Key step was a Wolff bromoketone synthesis performed on the intermediate longamide B.     

Total synthesis of (±)-protoemetinol

A new approach to the benzo[a]quinolizidine alkaloid was described. Total synthesis of (±)-protoemetinol (1) was reported.