A novel and efficient total synthesis of (±)-physostigmine

Application of the Wittig olefination-Claisen rearrangement protocol for the total synthesis of (±)-physostigmine.     

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.     

A formal total synthesis of (±)-9-isocyanoneopupukeanane

A formal total synthesis of the marine sesquiterpene (±)-9-isocyanoneopupukeanane starting from the readily available monoterpene carvone has been accomplished employing a combination of intermolecular Michael addition-intramolecular Michael addition reaction and an intramolecular rhodium carbenoid C-H insertion reaction as key steps, and identifying the isopropenyl group as a masked hydroxy group.     

Efficient formal synthesis of (±)-axamide-1 and (±)-axisonitrile-1 via an intramolecular Hosomi-Sakurai reaction

A formal synthesis of (±)-axamide-1 and (±)-axisonitrile-1 was achieved by using an intramolecular Hosomi-Sakurai reaction of the allylsilane derivative, as a key step, in which [(3-but-3-en-1-yl-3-methylcyclohex-1-en-1-yl)methyl](trimethyl)silane was transformed to a bicyclic compound possessing a core carbon framework under the oxidative dihydroxylation reaction conditions, in one step.     

Total synthesis of (±)-brazilin and formal synthesis of (±)-brazilein, (±)-brazilide A using m-CPBA

Total synthesis of (±)-brazilin has been accomplished. m-CPBA epoxidation of allyl alcohol 10 and epoxy opening reaction mediated by m-chlorobenzoic acid, formed in situ as a byproduct, gave advanced intermediate diol 14. O-alkylation and cyclization gave phenol 6 which enabled the formal synthesis of (±)-brazilein and (±)-brazilide A.     

A short synthesis of (±)-tecomanine via a Pauson-Khand-based route

The N-carboethoxy precursor to (±)-tecomanine has been prepared in 11 steps from 2-methyl-1-buten-3-yne. The key step, Pauson-Khand cyclization of a methylated 5-aza-6-nonen-1-yne succeeds, but only in low yield, a consequence of the dialkyl substitution about the azaenyne framework. Nevertheless, the overall sequence to that point is one of the more efficient to be described.     

Consecutive sigmatropic rearrangements in the enantioselective total synthesis of (−)-joubertinamine and (−)-mesembrine

Joubertinamine and mesembrine are two related alkaloids isolated from Sceletium plants. From the perspective of chemical synthesis, the major challenge posed by joubertinamine and mesembrine is undoubtedly the construction of the benzylic quaternary stereogenic center. We became intrigued by the prospect of applying successive sigmatropic rearrangements to build the key structural features of these alkaloids in enantioselective manner. In this article, we detail our results in this area, which include the enantioselective total synthesis of (−)-joubertinamine and (−)-mesembrine.     

Alkynes to (E)-enolates using tandem catalysis: stereoselective anti-aldol and syn-[3,3]-rearrangement reactions

A new tandem catalysis strategy that transforms alkyne derivatives to (E)-enol-equivalents followed by stereoselective anti-selective aldol coupling or syn-selective [3,3]-rearrangement transformations is reported. The mechanism is thought to proceed through an interchanging series of Lewis acid and Brønsted acid catalyzed reactions via the intermediacy of a ketiminum ion species.     

Protoilludane sesquiterpenes: synthesis of (±)-cerapicol, formal synthesis of (±)-sterpurene, and synthesis and absolute configuration of (+)-cerapicol

New approaches to the protoilludane sesquiterpenes (±)-cerapicol and (±)-sterpurene via rearrangement routes are described. The absolute configuration of (+)-cerapicol has been determined and found in accord with a biosynthesis of the natural product via cyclization of humulene to the so-called protoilludyl cation and a subsequent 1,2-alkyl shift.     

One-step biomimetic synthesis of (±)-linderaspirone A and (±)-bi-linderone

A one-step biomimetic synthesis of racemic linderspirone and bi-liderone from methyllinderone has been achieved, which probably reflects the biosynthesis of the natural products. There are few naturally occurring substances that appear to be formed by a [4+4] or [4+2] cycloaddition. We proposed that the [4+4] dimerization of methyllinderone proceeds via a stepwise mechanism involving a diradical intermediate.     

Efficient synthesis of cyclopentenones from enynyl acetates via tandem Au(I)-catalyzed 3,3-rearrangement and the Nazarov reaction

A highly efficient method for the synthesis of versatile cyclopentenones from readily available enynyl acetates via tandem Au(I)-catalyzed 3,3-rearrangement and the Nazarov reaction is developed. Significant substrate flexibility and excellent control of the double bond position in the cyclopentenone ring render this an attractive method for cyclopentenone synthesis.     

A facile three-step synthesis of (±)-crispine A via an acyliminium ion cyclisation

A high yielding cyclisation of the readily available N-(4,4-diethoxybutyl)-2-(3,4-dimethoxyphenyl)acetamide to 8,9-bis(methyloxy)-2,3,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-5(1H)-one is described. The latter can be reduced with either AlH₃ or BH₃ to (±)-crispine A in an overall yield of 55%.     

First total synthesis of(±)-sepicanin A

<正>A facile approach for the first total synthesis of naturally occurring geranylated flavanoids sepicanin A has been obtained with total yield 16%starting from 2,4,6-trihydroxyacetophenone after four steps.The key step was the protic acids(HCl or p-TsOH)-catalyzed benzopyrone formation in a protic polar solvent by deprotection and cycUzation of chalcone in one step.     

Formal total synthesis of (±)-cortistatin A

A second-generation synthesis of the pentacyclic core of the cortistatins, a family of rearranged steroidal alkaloids that have recently attracted much attention, is reported. The improved sequence provides access to significant quantities of this key compound, which enabled a formal total synthesis of (±)-cortistatin A by conversion to the key Nicolaou/Hirama dienone. It is anticipated that this new, robust route to the pentacyclic core will facilitate the total synthesis of a range of natural products in the cortistatin family, as well as the construction of key structural analogs to probe the promising biological activity of these important compounds.     

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.     

The total synthesis of (±)-arisugacin A

A 20-step total synthesis of (±)-arisugacin A with an overall yield of 2.1% is described here in detail. This synthesis features a formal [3+3] cycloaddition reaction of α,β-unsaturated iminium salts with 6-aryl-4-hydroxy-2-pyrones through a highly stereoselective 6π-electron electrocyclic ring-closure of 1-oxatriene. A strategic dihydroxylation-deoxygenation protocol leading to the desired angular C12a-OH was developed to serve as a critical step in leading to the final total syntheses of arisugacin A. This synthetic endeavor also led to an interesting and unexpected retro-aldol-aldol sequence in the AB-ring.     

A new total synthesis of (±)-oestrone

A conceptually new total synthesis of oestrone, based on a novel cascade of radical cyclisations from the iodo aryl vinylcyclopropane 2, via 10, 15, 16 and 17, leading to the intermediate trans,anti,trans-oestradiol derivative 11 in one step, is described. Oxidation of 11, followed by demethylation of the resulting aryl methyl ether 18 then gives (±)-oestrone 1.     

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.     

A concise synthesis of (±) and a total synthesis of (+)-epiquinamide

A total synthesis of the quinolizidine alkaloid (+)-epiquinamide 1 has been achieved starting from (−)-pipecolinic acid 3. The key step is the highly diastereoselective addition of a TBDMS-protected propargyl alcohol to a chiral aldehyde derived from 3 to give erythro alkynol 19, which is then easily transformed into the desired bicyclic skeleton.