Short and Divergent Total Synthesis of (+)-Machaeriol B, (+)-Machaeriol D, (+)-Δ(8)-THC, and Analogues.

Short and highly efficient stereoselective syntheses provide machaeriols and cannabinoids in a divergent approach starting from a common precursor, commercially available (S)-perillic acid. Key features of the novel strategy are a stereospecific palladium-catalyzed decarboxylative arylation and a one-pot sequence comprising a stereoselective hydroboration followed by oxidation or reduction of the corresponding intermediary boranes. The divergent approach is convincingly demonstrated by the five-step syntheses of (+)-machaeriol B, (+)-machaeriol D, and related analogues, and the four-step synthesis of (+)-Δ(8)-THC and an analogue.

Total synthesis of resveratrol-based natural products using a palladium-catalyzed decarboxylative arylation and an oxidative Heck reaction.

Controlled access to resveratrol-based natural products is offered by a novel, modular concept. A common building block readily available on a large scale serves as the starting material for the introduction of structurally important aryl groups by a Pd-catalyzed decarboxylative arylation and an oxidative Heck reaction with good yields and high stereoselectivity. The modular approach is convincingly documented by the successful synthesis of three racemic resveratrol-based natural products (quadrangularin A, ampelopsin D, and pallidol).

Alkali base-initiated Michael addition/alkyne carbocyclization cascades.

A new cascade reaction involving an intramolecular Michael addition followed by an alkyne carbocyclization is presented. The reaction is promoted by a substoichiometric amount of KHMDS and represents one of the rare examples where the carbocyclization of an unactivated alkyne is mediated by an alkali metal base, under mild conditions. The reaction allows the generation of functionally dense, stereochemically defined, tricyclic structures possessing three adjacent stereocenters in good yields and with high stereoselectivity.

A versatile protocol for the quantitative and smooth conversion of phosphane oxides into synthetically useful pyrazolylphosphonium salts.

A convenient protocol for the smooth conversion of the resistant P-O bond in phosphane oxides into a reactive P-N bond of synthetically useful pyrazolylphosphonium salts is described. A highly charged, oxophilic, phosphorus-centered trication is employed and the reactions are conducted at room temperature with quantitative yields. The resulting pyrazolylphosphonium cations are valuable synthetic intermediates and are used for the synthesis of a variety of organophosphorus compounds.