Tungsten-Promoted Intramolecular Alkoxycarbonylation for Synthesis of Complex Oxygenated Molecules

Pd-catalyzed diastereoselective allylation of aldehydes with 3-bromomethyl-5H-furan-2-one: stereoselective synthesis of β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones with a syn configuration

An efficient and diastereoselective Pd-catalyzed method of allylation of aldehydes with 3-bromomethyl-5H-furan-2-one is described. The proposed method allows the synthesis of β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones with a syn relative configuration for the first time.

Stereoselective synthesis of β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones

Zinc or a chromium(II) source with 3-(bromomethyl)furan-2(5H)-one (3) and an aldehyde gives β-(hydroxymethylaryl/alkyl)-α-methylene-γ-butyrolactones 5 in good yields and high diastereoselectivities. The methodology is demonstrated in concise syntheses of (±)-hydroxymatairesinol (8) and (±)-methylenolactocin (10) by subsequent arylboronate conjugate addition and translactonization, respectively.

The renaissance of alpha-methylene-gamma-butyrolactones: new synthetic approaches

The amount of research activity concerning alpha-methylene-gamma-butyrolactones and alpha-alkylidene-gamma-butyrolactones has increased dramatically in recent years. This Review summarizes the structural types, biological activities, and biosynthesis of these compounds, concentrating on publications from the past 10 years. Traditional approaches to alpha-methylene-gamma-butyrolactones and alpha-alkylidene-gamma-butyrolactones are then reviewed together with novel approaches, including those from our own research group, reported more recently.

Synthesis of bicyclic pyrane derivatives via tungsten-mediated [3 + 3] cycloaddition of epoxides with tethered alkynes

Propargyltungsten compounds bearing a tethered epoxide were prepared in short steps from readily available materials. In the presence of various Lewis acids, BF(3).Et(2)O catalysts (25 mol %) most effectively promote the [3 + 3] cycloaddition of the epoxide with its tethered propargyltungsten group, delivering bicyclic pyranyltungsten compounds in reasonable yields. This cyclization proceeds highly diastereoselectively with tolerance of various functional groups. The stereochemical outcome indicates that the cycloaddition is initiated by the ring opening of the epoxides via an exo-attack of the propargyltungsten group. The resulting pyranyltungsten organometallics were demetalated to yield various bicyclic pyranyl derivatives using different oxidants. This new method provides a short enantiospecific synthesis of bicyclic oxygen compounds if chiral epoxide is used in the cyclization. A mechanistic model is presented to rationalize the reaction pathway of this [3 + 3] cycloaddition.

Stereocontrolled synthesis of acyclic 1,3-diols via condensation of tungsten-syn-pi-pentadienyl complexes with aldehydes. A new Prins reaction via s-trans-diene cationic intermediates

In the presence of BF(3).Et(2)O, condensation of CpW(CO)(2)(syn-pi-2-methoxycarbonylpentadienyl) with aldehydes generated tungsten-eta(4)-trans-diene cation in cold toluene, and hydrolysis of this salt afforded tungsten-pi-allyl-anti-1,3-diols in good yields. This new synthesis of anti-1,3-diols represents an atypical Prins reaction that is applicable to normal aldehydes. The anti/syn ratios of 1,3-diols increased with an increase in the size of the aldehydes. These anti-1,3-diols were transformed into various complex oxygen heterocycles based on two demetalations: (1) conversion to an allyl cation followed by nucleophilic attack and (2) condensation with aldehydes via its CpW(NO)Cl derivative, to give functionalized alpha-methylene butyrolactones. A semi-emperical calculation was performed to deduce the transition-state structure to rationalize the anti-stereoselectivity.

Total Synthesis of Natural Bicyclic Lactones (+)-Dihydrocanadensolide, (+/-)-Avenociolide, and (+/-)-Isoavenociolide via Tungsten-pi-Allyl Complexes

A synthetic method using tungsten-pi-allyl compounds is developed for total syntheses of natural bislactones including (+)-dihydrocanadensaolide (2), (+/-)-avenociolide (3), and (+/-)-isoavenociolide (4). Syntheses of these natural compounds are based on a common intermediate, trans-alpha-methylene butyrolactones bearing an anti-homoallylic alcohol. The kep steps in the syntheses involve an intramolecular alkoxycarbonylation of propargyltungsten complexes to yield tungsten-pi,gamma-lactonyl species, followed by condensation of their CpW(NO)I(pi-allyl) derivatives with suitable aldehydes. This new method is very efficient for the synthesis of (+/-)-avenociolide (3) and (+/-)-isoavenociolide (4). Total syntheses of compounds 3 and 4 require only six and three steps, respectively, on the basis of chloropropargyl derivatives.