An approach to the skeleton of the securinega alkaloids. The total synthesis of (+/-)-securinine

[structure: see text]. The concise total synthesis of securinine in nine steps from readily available starting materials is described. Key steps of the synthesis include an addition of a silyloxyfuran to an in situ generated iminium ion and a novel ring closing metathesis reaction.     

An effective enantioselective approach to the securinega alkaloids: total synthesis of (-)-norsecurinine

[reaction: see text] A highly versatile approach to the enantioselective synthesis of securinega alkaloids is presented. Crucial steps are a palladium-catalyzed enantioselective imide alkylation, a vinylogous Mannich reaction, and a ring-closing metathesis process. Through this strategy, the synthesis of (-)-norsecurinine has been accomplished in nine steps and 11% overall yield.     

First asymmetric total synthesis of (+)-sparteine

[reaction: see text] The total synthesis of (+)-sparteine was accomplished from 2,5-norbornadione in 15 steps and 15.7% overall yield. The key steps were two ring-expansion reactions, one involving an intramolecular Schmidt reaction and one using a novel variant of the photo-Beckmann rearrangement.     

Synthetic studies on pseudolaric acid B:Enantioselective synthesis of C4,C10-di-epi-trans-fused[5-7]-bicyclic skeleton

Studies on the synthesis of antifungal and anticancer natural product,pseudolaric acid B,have led to the enantioselective synthesis of di-epi-trans-fused [5-7]-bicyclic co re skeleton.The synthesis was achieved in 10 linear steps,which features the Sharpless asymmetric epoxidation,cyanide-opening reaction of epoxide,and intramolecular [5+2] cycloaddition reaction as the key transformations.The stereochemistry was determined by the X-ray crystallographic analysis.     

Concise, enantioselective total synthesis of (-)-alstonerine

A novel enantioselective total synthesis of (-)-alstonerine has been completed that requires only 15 steps from L-tryptophan. The synthesis features the first application of a Pauson-Khand reaction to synthesize an azabridged bicyclic skeleton. [reaction: see text]     

Rapid synthesis of the N-methylwelwitindolinone skeleton

An efficient, convergent synthesis of the core bicyclo[4.3.1]decane ring system of welwitindolinones is described. Key steps in the synthesis include an intramolecular palladium-catalyzed enolate arylation reaction to create the desired bicyclic skeleton and a Curtius rearrangement to install the bridgehead isocyanate unit. [reaction: see text]     

A triple diene-transmissive Diels-Alder strategy to build the quassinoid framework

[chemical reaction: see text]. An advanced intermediate to the highly oxygenated triterpene quassinoids was prepared in 14 steps from tetrahydrofuran. The key steps are three diene-transmissive Diels-Alder cycloadditions. Several features of this synthesis are noteworthy, including a successful Mitsunobu reaction on an allenylic alcohol, a rare [4 + 2] cycloaddition involving an enethiol ether dienophile, and complete control over all 10 chiral centers created.     

A highly enantioselective synthesis of (−)- and (+)-juglomycin A through Dötz annulation and asymmetric dihydroxylation

A highly enantioselective synthesis of (−)- and (+)-juglomycin A, a quinone antibiotic is described. The synthesis is completed in eight steps, and 19% overall yield and in a high enantioselectivity of 99.5% [for (−)-juglomycin A] and 98.5% [for (+)-juglomycin A]. The synthetic strategy features an efficient combination of the Dötz annulation reaction and asymmetric dihydroxylation as the keys steps.     

Synthesis of the C(2)-C(13) fragment (the A-B spiroketal unit) of spongistatin 1 (altohyrtin A): use of a common intermediate for the synthesis of both spongistatin spiroketals

[reaction: see text] A convergent synthesis of 14 corresponding to the A-B spiroketal core of spongistatin 1 has been accomplished via an iodo-spiroketalization reaction of glycal 9, which was synthesized in three steps from a late-stage intermediate used in our synthesis of the C-D spiroketal fragment of spongistatin 1. Elaboration of 14 to the A-B spiroketal 15 was accomplished in three steps.     

Total synthesis of (+)-epiquinamide

The stereoselective total synthesis of the novel quinolizidine alkaloid (+)-epiquinamide is presented, starting from the amino acid l-allysine ethylene acetal. Key steps in the synthesis involved a highly diastereoselective N-acyliminium ion allylation and a ring-closing metathesis reaction to provide the bicyclic skeleton. [reaction: see text]     

Total synthesis of (+)-cyanthiwigin U

A concise total synthesis of the tricyclic terpene cyanthiwigin U has been accomplished in 12 steps and 17% overall yield. The key step of the synthesis is a two-directional tandem metathesis reaction that forms the cyclohepta[e]indene core from a readily available bicyclo[2.2.2]octene.     

Efficient asymmetric synthesis of (+)-SCH 351448

An efficient and stereocontrolled total synthesis of (+)-SCH 351448, a novel activator of low-density lipoprotein receptor promoter, has been achieved with a longest linear sequence of 21 steps. Key steps include applications of the recently developed asymmetric allyl- and crotylsilane reagents and a new protodesilylative version of the tandem silylformylation/allylsilylation reaction, which provides an efficient synthesis of 1,5-syn-diols. [reaction: see text]     

Enantioselective synthesis of 15-epi-haterumalide NA methyl ester and revised structure of haterumalide NA

[structure: see text] The enantioselective synthesis of the enantiomer of the haterumalide NA methyl ester, a cytotoxic macrolide from an Okinawan sponge, was achieved from the threitol derivative in 26 steps. The key steps are the stereoselective construction of a chloroolefin unit and the intramolecular Reformatsky-type reaction. This synthesis revised the absolute stereochemistry of haterumalide NA.     

Synthesis of the integrastatin nucleus using the Ramberg-Bäcklund reaction

[reaction: see text] The first synthesis of the tetracyclic nucleus of the Integrastatins, natural products that have been shown to selectively inhibit HIV-1 integrase, is reported. Key steps of this synthesis involve a novel cis-selective Ramberg-B?cklund reaction and an unusual Lewis acid-promoted cyclization step.     

Concise total synthesis of (+/-)-aloperine and 6-epi-aloperine

[reaction: see text] Total synthesis of aloperine and 6-epi-aloperine is reported. The crucial steps of the synthetic strategy are an aza-annulation reaction and an intermolecular Diels-Alder reaction. The synthetic plan proceeds from commercially available piperidine-2-ethanol.     

Approach to the synthesis of cladiell-11-ene-3,6,7-triol

[reaction: see text] The synthesis of an advanced intermediate in the synthesis of the title compound has been achieved. Key steps include an Ireland-Claisen rearrangement to install the C7 tertiary alcohol stereocenter, an SN2' reaction of an alkoxymethyl Cu reagent, and a diastereoselective Re-catalyzed allylic alcohol transposition.     

Application of RCM reaction in the construction of ABC ring of micrandilactone A

[reaction: see text] The functionalized ABC ring system of micrandilactone A was successfully constructed in 14 steps. The key reactions in this synthesis are the intermolecular Diels-Alder reaction (IMDA) and the eneyne ring-closing metathesis (RCM) reaction.     

Total synthesis of caerulomycin C via the halogen dance reaction

[reaction: see text] The total synthesis of caerulomycin C is described. Key steps in this synthesis utilize 1,2-, 1,3-, and 1,4-halogen dance reactions for the functionalization of the pyridine ring.     

Total Synthesis of (+)-okaramine J featuring an exceptionally facile N-reverse-prenyl to C-prenyl aza-Claisen rearrangement

[reaction: see text] The convergent total synthesis of (+)-okaramine J was achieved in a longest linear sequence of 12 steps from l-tryptophan tert-butyl ester. A key reaction was the acid-catalyzed room-temperature aza-Claisen rearrangement of a N-reverse-prenylated hexahydro[2,3-b]pyrroloindole to a C-prenylated derivative.     

Total synthesis of (-)-martinellic acid via radical addition-cyclization-elimination reaction

The asymmetric total synthesis of martinellic acid, the first pyrrolo[3,2-c]quinoline alkaloid found in nature, is described. Three key steps in our synthesis of (-)-martinellic acid are the Bu(3)SnH-promoted radical addition-cyclization-elimination (RACE) reaction of an oxime ether with an alpha,beta-unsaturated ester to generate the pyrrolo[3,2-c]quinoline core, a chemoselective lactam carbonyl reduction, and guanidinylation under Mitsunobu reaction conditions. The key radical cyclization has also been investigated by using SmI(2). (-)-Martinellic acid was synthesized from commercially available methyl 4-bromo-3-methylbenzoate in fewer steps than previous syntheses and in an improved overall yield.