Total synthesis of Carpatamides A–D

A synthetic strategy was developed for the synthesis of the common core structure of Carpatamides A–D. The total synthesis of Carpatamides A and C was completed in 6 steps and of Carpatamides B and D in 7 steps, by employing the Wittig olefination, olefin cross metathesis and acid amine coupling reactions as key steps.     

Total synthesis of lamellarins D, H, and R and ningalin B

A concise total synthesis of lamellarins D (7 steps), H (7 steps), and R (5 steps) and ningalin B (5 steps) is achieved starting from the corresponding aldehydes and amines. The synthesis features three oxidative reactions as key steps in a biomimetic manner, involving an AgOAc-mediated oxidative coupling reaction to construct the pyrrole core, a Pb(OAc)(4)-induced oxidative cyclization to form the lactone, and Kita's oxidation reaction to form the pyrrole-arene C-C bond.     

A six-step synthetic approach to marine natural product (+)-aureol

A concise synthetic approach to the marine natural product (+)-aureol has been achieved from readily available starting materials using obviously fewer steps in comparison to the related report in literature (6 steps versus 12 steps from (+)-sclareolide). Key steps of this protocol include a boron trifluoride-catalyzed domino 1,2-H and 1,2-methyl shifts and a nickel(II)-catalyzed cross-coupling reaction between an alkyl iodide and an aryl Grignard reagent.     

Biomimetic Total Synthesis of (±)‐Homodimericin A

A biomimetic total synthesis of racemic homodimericin A was achieved in seven steps, including two cascade reactions. Aqueous buffer solutions are found to help both the oxidative dimerization cascade and the intramolecular Diels–Alder cascade. This synthetic sequence validates key steps in the biogenetic proposal of homodimericin A.     

Biomimetic Total Synthesis of (±)-Homodimericin A

A biomimetic total synthesis of racemic homodimericin A was achieved in seven steps, including two cascade reactions. Aqueous buffer solutions are found to help both the oxidative dimerization cascade and the intramolecular Diels–Alder cascade. This synthetic sequence validates key steps in the biogenetic proposal of homodimericin A.     

Syntheses of strychnine, norfluorocurarine, dehydrodesacetylretuline, and valparicine enabled by intramolecular cycloadditions of Zincke aldehydes

A full account of the development of the base-mediated intramolecular Diels-Alder cycloadditions of tryptamine-derived Zincke aldehydes is described. This important complexity-generating transformation provides the tetracyclic core of many indole monoterpene alkaloids in only three steps from commercially available starting materials and played a key role in short syntheses of norfluorocurarine (five steps), dehydrodesacetylretuline (six steps), valparicine (seven steps), and strychnine (six steps). Reasonable mechanistic possibilities for this reaction, a surprisingly facile dimerization of the products, and an unexpected cycloreversion to regenerate Zincke aldehydes under specific conditions are also discussed.     

Efficient synthetic method of Psammaplin A

A new concise and efficient synthetic method of Psammaplin A was developed. Psammaplin A was obtained with 50% overall yield in nine steps from p-hydroxybenzaldehyde and ethyl acetoacetate via Knoevenagel condensation and direct nitrosation as key steps. This method might be very efficient to construct a quite diverse library of Psammaplin A type analogs.     

An Efficient Synthesis of Selective Human NR2A Antagonist NVP-AAM077

A short and efficient synthesis of the selective human N-methyl-D-aspartate （NMDA） receptor 2A （NR2A） antagonist NVP-AAM077 is described. The target was achieved in 8 steps and in 54% overall yield from the commercially available chemical 3-methylbenzene-1,2-diamine. A NaIO4/DMF-based oxidation of the bromide to corresponding aldehyde and an addition of phosphinic acid ester to the aldimine successfully served as the key steps.     

Asymmetric induction of conduritols via AAA reactions: synthesis of the aminocyclohexitol of hygromycin A

Two synthetic routes towards the construction of the aminocyclohexitol moiety of hygromycin A have been developed based on palladium-catalyzed asymmetric alkylation of conduritol derivatives. A protocol has been established whereby this biologically relevant molecule is formed from benzoquinone. A conduritol A derivative is synthesized in eight steps from benzoquinone and is then subjected to the palladium reaction. From this flexible intermediate, four epimers of the aminocyclitol, including the natural one, can be obtained with complete stereoselectivity. Racemic conduritol B derivatives are available in four steps from benzoquinone, and these are then made enantiomerically pure by a palladium-catalyzed dynamic kinetic resolution. From the chiral conduritol B, the aminocyclitol is available in six steps. Excellent levels of enantio- and diastereoselectivity highlight these strategies.     

Unified total synthesis of the natural products endiandric acid A,kingianic acid E,and kingianins A,D, and F

A measure of the strength of a synthetic strategy is its versatility: specifically, whether it allows structurally distinct targets to be prepared. Herein we disclose a unified approach for the total synthesis of natural products of three distinct structural types, all of which occur naturally as racemic mixtures. The point of divergence involves the terminal alkylation of a conjugated tetrayne, and culminates in a significantly shortened synthesis of endiandric acid A (8 steps), the first total synthesis of kingianic acid E (8 steps), and a second-generation synthesis of kingianins A, D, and F (11 steps). Evidence for redox catalysis in the biosynthesis of kingianic acid E is presented.     

Palladium-catalyzed synthesis of 1,2-dihydro-4(3H)-carbazolones. Formal total synthesis of murrayaquinone A

Two sequential palladium-catalyzed reactions are the key steps in a novel synthetic route to 1,2-dihydro-4(3H)-carbazolones. The steps are an intermolecular Stille cross-coupling followed by a reductive N-heteroannulation. A formal total synthesis of murrayaquinone A, employing this sequence, is reported.     

Synthesis of hexacyclic parnafungin A and C models

A convergent, practical route to unstable hexacyclic parnafungin A and C models has been developed. Two iodoxanthones were prepared in four or five steps (33-50% overall yield). Suzuki-Miyaura coupling of the iodoxanthones with excess readily available 3-carbomethoxy-2-nitrophenyl pinacol boronate afforded the hindered highly functionalized 2-arylxanthones (53-58%) in the first key step. In the second key step, zinc reduction gave benzisoxazolinones that were treated with MsCl and then base to generate the unstable hexacyclic parnafungin A (13% overall yield for 8 steps) and C (8% overall yield for 9 steps) models. Analogously to the parnafungins, hexacyclic parnafungin C model decomposes to a phenanthridine with a half-life of 2 d in CDCl(3).     

Total synthesis of (+)-nakadomarin A

The total synthesis of (+)-nakadomarin A is described. A three-component cycloaddition of a hydroxylamine, aldehyde, and cyclopropane to form a highly functionalized tetrahydro-1,2-oxazine serves as the foundation for this synthesis. The resulting oxazine is formed as a single diastereomer with the absolute configuration being dictated by the chirality of the cyclopropane. Other key steps include: desymmetrization of a malonate by reduction, Heck cyclization and pyrrolidine formation, and ring-closing metathesis to form both cycloalkenes. Overall, the synthesis required 23 linear steps from the cyclopropane, which in turn is available (six steps) in optically pure form from commercially available d-mannitol.     

Total synthesis of (-)-leuconicine A and B

Concise asymmetric total syntheses of Strychnos alkaloids (-)-leuconicine A (14 steps, 9% overall yield) and B (13 steps, 10% overall yield) have been accomplished. Key steps include (1) our sequential one-pot spiro-cyclization/intramolecular aza-Baylis-Hillman method to prepare the ABCE framework; (2) a novel domino acylation/Knoevenagel cyclization to prepare the F-ring; and (3) a Heck cyclization to access the D-ring.     

Total synthesis of (±)-cortistatin J from furan

A concise, diastereoselective total synthesis of (±)-cortistatin J has been completed in 20 steps from furan. Key steps include an intramolecular [4 + 3] cyclization of a disubstituted furan with a (Z)-2-(trialkylsilyloxy)-2-enal to construct the tetracyclic core and a (Z)-vinylsilane/iminium ion cyclization to form the A ring.     

Short diastereoselective synthesis of the C1-C13 (AB spiroacetal) and C17-C28 fragments (CD spiroacetal) of spongistatin 1 and 2 through double chain-elongation reactions

A unique and practical synthetic sequence for rapid access to polyketides and to further the spiroacetals derived from them, which utilizes a bidirectional Hosomi-Sakurai allylation approach around key allylsilanes in the synthesis of the AB and CD ring systems of spongistatin 1 and 2, is reported. The synthesis of the AB spiroacetal 9 requires 13 steps, with a longest linear sequence of seven steps in an overall yield of 27%. The synthesis of the CD spiroacetal 13 requires 15 steps, with a longest linear sequence of 11 steps in an overall yield of 30%. Both syntheses start from but-3-enol.     

Synthesis and complete stereochemical assignment of psymberin/irciniastatin A

We describe a concise and flexible synthetic avenue for the preparation of compounds with structures relevant to those proposed for the novel marine-derived differential cytotoxins psymberin and irciniastatin A. Our efforts led to their complete stereochemical assignment and the notion that psymberin and irciniastatin A are identical compounds. Our total synthesis features an interesting termini-differentiating lactolization of a dialdehyde obtained from a C2-symmetrical bis-olefin precursor, a mild platinum-catalyzed hydrolysis of an epimerizable nitrile, a novel protocol to prepare sensitive methyl imidates, and a one-pot conversion of these imidates to N-acyl aminals. Starting from fragments 5-7 (prepared in 7-8 steps each, 30-49% overall yield) the synthesis of psymberin/irciniastatin A was completed in an additional 9 steps and 30% yield (17 steps longest linear sequence, 8.9% overall).     

Highly efficient asymmetric synthesis of fluvirucinine A1 via Zr-catalyzed asymmetric carboalumination of alkenes (ZACA)-lipase-catalyzed acetylation tandem process

ZACA-lipase-catalyzed acetylation tandem process has been shown to proceed satisfactorily with either TBS-protected 4-penten-1-ol or 3-buten-1-ol to provide the corresponding enantiomerically pure (R)-2-ethyl-1-alkanols. Either (R)-5 or (R)-6 was converted to 3 in seven steps. The other fragment 4 was synthesized in nine steps from (-)-(S)-citronellol. Conversion of 3 and 4 into 99% pure fluvirucinine A1 was achieved in four steps via amidation-ring closing metathesis, the overall yield in the longest linear sequence being 34% (13 steps).     

Diastereoselective reactions at enantiomerically pure, sterically congested cyclohexanes as an entry to wailupemycins A and B: total synthesis of (+)-wailupemycin B

Wailupemycin A (1) and B (2) are polyketide natural products with a highly substituted cyclohexanone core. Three different routes for the syntheses of these compounds were pursued, which commenced from either (R)-(-)-carvone (ent-5) or (S)-(+)-carvone (5). In the first approach it was attempted to construct the skeleton of wailupemycin A from triol 19 (nine steps from ent-5; 19 % yield) by a sequence of diastereoselective epoxidation, nucleophilic ring opening at C-13 and carbonyl addition at C-5. The synthetic plan failed at the stage of the carbonyl addition to aldehyde 27, which had been obtained in seven steps (18 % yield) from triol 19. The second route included an epoxide ring opening at C-13 and a carbonyl addition at C-7 as key steps. It could have led to either wailupemycin A or B depending on the diastereoselectivity of the addition step. Starting from allylic alcohol 30 (six steps from ent-5; 59 % yield) the cyclohexanone 28 was obtained in five steps (54 % yield). Unfortunately, the carbonyl addition failed also in this instance. In the eventually successful third attempt the skeleton of wailupemycin B was built from cyclohexanone 43 (eight steps from 5; 53 % yield) by highly diastereoselective carbonyl addition reactions at C-7 and C-12. The phenyl group at C-14 was introduced at a late stage of the synthetic sequence. Careful protecting group manipulation finally allowed for the total synthesis of (+)-wailupemycin B. The absolute and relative configuration of the natural product was unambiguously confirmed. The total yield of wailupemycin B amounted to 6 % over 23 steps starting from (S)-(+)-carvone (5).     

An expeditious synthesis of (+/-)-desepoxy-4,5-didehydromethylenomycin a methyl ester

[formula: see text] A total synthesis of the racemic methyl ester of desepoxy-4,5-didehydromethylenomycin A has been achieved in six steps with an overall yield of 31% starting from diethyl methanephosphonate. The key steps include the Nazarov cyclization of the dienone 7 leading to the alpha-phosphoryl cyclopentenone 8 and the Horner-Wittig reaction of the latter employed for the introduction of the exocyclic methylene moiety.