Biogenetically-inspired aromatisation of a steroid D-ring

The androstenolone derivative (4) has been converted to the aromatic ring D ketone (16), in which the former C/D angular methyl is incorporated into the new D-ring, as in biosynthesis of $\text{Nicandra}$ steroids.     

Total synthesis of flustramine C via dimethylallyl rearrangement

The marine natural product flustramine C from the bryozoan Flustra foliacea was synthesized in five steps and 38% yield starting from Nb-methyltryptamine. The key step is the biomimetic oxidation of the natural product deformylflustrabromine causing selective 1,2-rearrangement of the inverse prenyl group. By 1H,15N HMBC experiments, it is unambiguously shown that the reaction with t-BuOCl commences with chlorination of the side chain nitrogen. Deformylflustrabromine itself was synthesized via Danishefsky inverse prenylation. [reaction: see text].     

New synthesis of a chiral steroid cd-ring synthon by means of enantioselective double Michael addition

A new synthetic method of (+)-(1R)-acetyl-(7aR)-methyl-4-hydroinden-5-one (2) by highly enantioselective double Michael addition involving alkenylcopper-phosphine complex, 3-trimethylsilylbutenone and 2-methyl-2-cyclo-pentenone is presented.     

Amphidinolide B: asymmetric synthesis of a C7-C20 synthon

[reaction: see text] An asymmetric synthesis of a C(7)-C(20) synthon of amphidinolide B is described. The synthesis entails the construction of C(7)-C(13) and C(14)-C(20) fragments and makes extensive use of catalytic asymmetric bond constructions to establish the requisite stereochemical relationships. Fragment coupling proceeds by Suzuki cross-coupling and installs the trisubstituted diene unit that is among amphidinolide B's defining structural features.     

Total synthesis of (+)-blennolide C and (+)-gonytolide C via spirochromanone

We report the asymmetric total synthesis of (+)-blennolide C and (+)-gonytolide C isolated from endophytic fungi. The synthesis involved construction of a spirochromanone with a chiral quaternary carbon by the aldol reaction of o-hydroxyacetophenones and optically active α-oxygenated cyclohexenone, followed by cyclization under acidic conditions. Oxidative cleavage of the alkene moiety of the spirochromanone furnished the chromanone diester. Through treating the diester with a Lewis acid, the first total synthesis of (+)-blennolide C was achieved by deprotecting the oxygen functionality of the diester and simultaneous Dieckmann condensation. Total synthesis of (+)-gonytolide C was also achieved by lactone formation from the deprotected diester.     

Towards the synthesis of massadine: a unified strategy for the stereoselective synthesis of the carbocyclic C,D-ring subunit

Massadine is a hexacyclic marine natural product, which belongs to the family of pyrrole-imidazole alkaloids. Herein, we describe a unified approach to the C,D-ring subunit of this sponge metabolite based on the exploitation of a norbornene scaffold for the stereocontrolled construction of massadine's carbon skeleton. Highlights of the sequence presented include the application of a stereospecific norbornyl rearrangement for facile introduction of an oxygen at the C7-position within the norbornene nucleus, a highly regioselective and end group differentiating ozonolytic scission of a C-C double bond, and an oxidative decarboxylation reaction for the installation of the hindered secondary C2-alcohol function. Furthermore, the iterative assembly of the two guanidine entities as well as the implementation of the spirocyclic junction between the C- and the D-rings are described. Collectively, these key transformations permit an entry to an appropriately functionalized carbon framework, which will serve as a starting point for our efforts toward the completion of the synthesis of massadine.     

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 valeriananoids A, B, and C via autocatalytic diastereoselective domino Michael reaction

Natural enantiomers of unique tricyclic sesquiterpenoids, valeriananoids A-C 1-3, have been synthesized starting from bicyclo[2.2.2]octane-2,5-dione derivative 11, which was obtained by diastereoselective catalytic domino Michael reaction of oxophorone 5 with 8-phenylmenthyl acrylate 10 by LDA or silica-gel-base (NMAP-Li). The tricyclic ring was closed selectively by intramolecular 6-endo-trig mode cyclization of the ketyl radical, which was generated from keto-allylether 25 by either lithium or sodium naphthalenide.     

A new one-pot synthesis of all E-retinoic acid via a new enaminodiester synthon

A ‘one-pot’ synthesis of allE-retinoic acid from a new enaminodiester was described. The enaminodiester was easily produced from methyl isopropylidenemalonate and DMF-DMA.     

Total synthesis of steroid analogues by organometallic procedures

The synthesis of steroid-type structures has been achieved by means of a series of coupling, alkylation, carbonylation and cyclization steps, all of which involve organometallic reagents or catalysts. The ring closures are effected with carbonyl complexes of nickel and with tin tetrachloride. The X-ray structure of the main product resulting from two successive cyclizations is described.     

Total synthesis of actinomycin D(C1) via a ring-opening reaction of aziridine

Actinomycin D(C₁) has been synthesized by a route involving the ester formation between two peptide fragments, (2S,3S)-1-(2-nitro-3-benzyloxy-4-methylbenzoyl)-3-methyl-2-aziridine-carbonyl-D-valylproline t-butyl ester and N-benzyloxycarbonylsarcosyl-N-methylvaline, via a ring-opening reaction of aziridine. Cyclization, followed by reduction and oxidation, gave actinomycin D(C₁). The synthetic actinomycin D(C₁) was indistinguishable from natural substance with respect to physical properties and biological activity.     

Highly efficient one-pot synthesis of D-ring chloro-substituted neocryptolepines via a condensation—Pd-catalyzed intramolecular direct arylation strategy

D-ring chloro-substituted neocryptolepines have been synthesized in excellent yield starting from 3-bromo-2-chloro-1-methylquinolinium triflate via a one-pot condensation—Pd-catalyzed intramolecular direct arylation strategy involving chloroanilines. The 3-bromo-2-chloro-1-methylquinolinium triflate was obtained via methylation of commercial 3-bromo-2-chloroquinoline with methyl triflate.     

Total synthesis of leustroducsin B via a convergent route

Total synthesis of leustroducsin B was achieved via a convergent route, which includes Julia coupling reaction of segment A with segment B followed by Stille coupling reaction of segment C.     

Total synthesis of cryptophycin analogues via a scaffold approach

[reaction: see text] Allylation of in situ generated beta,gamma-unsaturated aldehydes affords rapid access to vinyl halide analogues of fragment A of the cryptophycins. Three scaffolds are prepared in gram quantities by a ring-closing metathesis approach. Derivatization via a variety of cross-coupling protocols is possible, which affords novel analogues of these potent antimitotic agents.     

Total synthesis of isoroquefortine C

A short and efficient total synthesis of isoroquefortine C, the 3,12-(Z)-isomer of roquefortine C, from L-tryptophan methyl ester hydrochloride and 4(5)-(hydroxy)methylimidazole hydrochloride is described.     

Total synthesis of greensporone C

The first total synthesis of greensporone C, a cytotoxic 14-membered resorcylic acid lactone, has been accomplished via a longest linear sequence of 16 steps in 3.3% overall yield. The key features of the synthesis include Mitsunobu esterification and ring-closing metathesis to construct the macrocycle and establish the (E)-olefin geometry, respectively. Our synthesis also confirmed the absolute stereochemistry of the natural product.     

Total synthesis of halichondrin C

The first total synthesis of halichondrin C has been completed, highlighted by development of the synthetic method to construct the C8-C14 polycycle. Cr-mediated coupling reactions are used seven times to form a new C-C bond. The acid stability of halichondrin C is studied, demonstrating that the macrolactone stabilizes the C8-C14 polycycle, relative to the one present in the C1-C16 model.     

Total synthesis of hoiamide C

Hoiamide C was synthesized in 16 steps with an overall yield of 1.8% starting from homoallylic alcohol 18, unambiguously confirming its structure.