The synthesis of leukotriene analogues via acetylene carbocupration

A general route to simple LTB₄ analogues is reported based on acetylene carbocupration followed by trapping with methyl 5-oxopentanoate.     

An efficient approach to the synthesis of 3-vinylidene tetrahydropyrans via Prins-type cyclization

Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes are described. The results obtained indicate that trimethylsilyl trifluoromethanesulfonate (TMSOTf) efficiently catalyses cyclization leading to the corresponding 3-vinylidene tetrahydropyrans in high yield as single isomers.     

New approach to the synthesis of 6-ketosteroids via organoiron complexes.

New Methodology is described for the synthesis 6-ketosteroids, of potential value for the synthesis of β-ecdysone, $\text{via}$ tricarbonyl (4-methoxy-1-methylcyclohexadienyl) iron hexafluorophosphate $\text{1}$.     

An efficient approach to the stereoselective synthesis of 2,6-disubstituted dihydropyrans via stannyl-Prins cyclization

A general method has been developed for the stereoselective construction of 2,6-disubstituted dihydropyrans based on the Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with vinylstannanes. This novel methodology was applied to the enantioselective total synthesis of (−)-centrolobine.     

New convenient synthesis of iridol. An approach to the synthesis of ubiquinones

A strategy for the synthesis of ubiquinones, in which iridol is the key intermediate, has been developed, together with a new convenient synthesis of iridol (2,3-dimethoxy-5-methylphenol) starting from the easily available 4-methylphenol and using mild conditions and friendly and high-yielding reactions.     

An approach to the synthesis of isolongifolene

An efficient synthesis of 7, 7-dimethyltricyclo [6.2.1.0^1,6] undeca-2, 5-dien-4-one 2, an advanced intermediate for the synthesis of the tricyclic sesquiterpene isolongifolene 1, has been carried out utilising Ar₁-5 participation reaction as the key step.     

An approach to the synthesis of stenine

A type 2 N-acylnitroso intramolecular Diels-Alder reaction followed by reductive N-O bond cleavage formed the B and C rings of the Stemona alkaloid stenine. Further elaboration provided the functionalized tricyclic core.     

An approach to the synthesis of the phomoidrides

The phomoidrides are a structurally fascinating family of natural products which possess moderate inhibitory activity against Ras farnesyl transferase and squalene synthase. Since their discovery they have inspired a great deal of attention from synthetic chemists. Our own work, culminating in an efficient synthesis of the fully elaborated tetracyclic core of phomoidrides B and D, is described herein. The synthesis relies on a late stage tandem reaction involving a novel carbonylation reaction that delivers the strained bicyclic pseudoester system, which strain in turn drives a highly efficient silyloxy-Cope rearrangement that delivers the tetracyclic core of phomoidrides B and D. Several examples of this powerful tandem reaction are presented that document its tolerance of significant structural variation. The application of this methodology to the synthesis of a phomoidride D precursor lacking only the maleic anhydride is described, and the prospects for the completion of a total synthesis are discussed.     

An approach to the synthesis of dimeric resveratrol natural products via a palladium-catalyzed domino reaction

A route for the rapid assembly of the carbon framework of several resveratrol natural products is presented. A palladium-catalyzed domino reaction of bromostilbene derivative 6 and tolane 7, involving two sequential Heck coupling reactions, provides access to the benzofulvene-based core of various resveratrol-derived natural products. The carbon skeleton of pallidol and its congeners is achieved by a Lewis acid-induced Nazarov-type oxidative cyclization of 9.     

An approach to the synthesis of pseudomonic acids

The synthesis of the cis-fused γ-lactone 2,7-dioxabicyclo-[4,3,0]non-4-en-8-one (3) by two routes is reported. Its stereoselective conversion to a key intermediate for pseudomonic acid synthesis is described.     

An approach to the total synthesis of welwistatin

An approach to the total synthesis of the antimicrotubule agent welwistatin is described. Key transformations include (1) a 7-endo intramolecular conjugate addition reaction of enone 6 to deliver the strained bicyclo[4.3.1]decanone 5; (2) a 6pi electrocyclic ring closure of trienecarbamate 16 followed by oxidation to afford protected aniline 17; and (3) an intramolecular cyclization of acetic acid derivative 18 to give rise to indole 19. [reaction: see text]     

An asymmetric approach to the synthesis of trans-dihydrindandione

A three-step asymmetric approach to the synthesis of (3aS,7aS)-3a,4-dihydro-7a-methyl-1,5(7aH)-indandione in 60% enantiomeric excess is described.     

The synthesis of deoxyfusapyrone. 1. An approach to the pyrone moiety

An effective synthesis of the C1-C10 component of deoxyfusapyrone has been achieved that will allow for the synthesis of both the (R) and (S) form of the C-8 chiral center starting from optically pure (+)- and (-)-3,3-dimethyl-2-hydroxy-gammalactone (pantolactone).     

An approach to the enantiocontrolled synthesis of pseudomonic acids via a novel mono—claisen rearrangement

A short, efficient approach to a key chiral intermediate for the synthesis of pseudomonic acids A and C is delineated.Pseudomonic acids A($\text{1a}$), B($\text{1b}$), and C($\text{2}$) are members of a novel of “C-glycopyranoside” antimicrobial agents which have recently attracted synthetic attetion.² Presently, we wish to report a short efficient stratedy towards the total synthesis of opticaly active pseudomonic acids. The sequence is highlighted by a novel controlled mono-Claisen rearrangement and a highly regioselective π-allylpalladium mediated displacement.Diacetyl-(L)-arabinal ($\text{3}$)³ was converted to the bis-ketenesilylacetal $\text{4}$ and warmed to 60°C according to the Ireland ester-enolate Claisen rearrangement method.⁴ Over a period of ≈5h, smooth conversion to a major rearranged product $\text{5}$ was observed by 300 MHz NMR. The identity of $\text{5}$ was confirmed by direct desilylation and methylation (KF, KHCO₃, H₂O, HMPA, CH₃I). After flash chromatography, compound $\text{7}$ was isolated in 55% overall yield from $\text{3}$. Careful inspection of the crude methylation product revealed the presence of ≈5% doubly rearranged product $\text{6}$.The rearrangement of $\text{4}$ to $\text{5}$ is a unique example of a selective mono-Claisen rearrangement in which the rate of a second similar Claisen rearrangement ($\text{5}$ → $\text{6}$) is much slower under the reaction conditions. Although the reasons for this interesting selectivity are unclear at this time,⁵ in practice, the mono-Claisen rearrangement obviates the need for selective differentiation of the two hydroxyl groups, a difficult task at best, in this case.Palladium mediated allylic acetate displacement provided an ideal method for introduction of a second chemodifferentiated side chain with allylic retention and retention of stereochemistry. Alkylation of $\text{7}$ with sodiothylmalonate using 5 mole % Pd(O)dppe₂⁶ was unusually facile (<45 min, 25°C, THF). After semi-preparative HPLC, essentially a single regio- and stereoisomer was isolated in 96% yield.⁷ Structure $\text{8}$ was confirmed by extensive ¹H-NMR decoupling, as well as an off-resonance ¹³C-NMR experiment. In particular, H₁ (δ 4.53) was coupled vicinally to H₆ and H₆′ (5 Hz, 8 Hz) and H₂ (1.5 Hz), and allylically to H₃ (2 Hz). In contrast, H₄ (δ 2.78) was coupled to H₇ (10 Hz), H_5e and H_5a (1.8 Hz, 4 Hz), H₃ (5 Hz), and H₂ (<1 Hz). In addition, H₁ and H₄ exhibited a small long range coupling constant (J = <1 Hz). The coupling constants rule out

regioisomer $\text{9}$ and are fully consistent with the indicated conformation, which minimizes 1,3-diaxial-like interactions.Finally, catalytic osmylation of $\text{8}{}^8$ gave a single cis-diol $\text{10}$ in nearly quantitative yield. Appending of suitably functionalized side chains to provide an enantiocontrolled synthesis of pseudomonic acids A($\text{1a}$) and C($\text{2}$) is in progress.^9,10     

Benzothiazines in organic synthesis. An approach to floresolide B

The intramolecular conjugate addition of a sulfoximine carbanion to an α,β-unsaturated ester results in the formation of a benzothiaine bearing a benzylic stereocenter with extremely high fidelity. We have used this methodology to complete a formal total synthesis of the antitumor agent (+)-floresolide B.