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A four-component coupling reaction of 3,5-dimethoxybenzyne with 2-methyl-2-cyclohexenylmagnesium chloride, carbon dioxide, and iodine was utilized as a key step in the first total synthesis of dehydroaltenuene B.

[reaction: see text] The synthesis of the highly substituted indole portion of the complex tremorgenic natural products lolicine A and B is presented. The Diels-Alder reaction of a quinone monoimine enables the synthesis of an appropriately substituted indole. The key step in the synthesis is a tandem isopropenyl cuprate addition/aldol cyclocondensation which provides the necessary functionality for elaboration to the 2,2,5,5-tetramethyltetrahydrofuran.

[reaction: see text] The ustiloxins are a family of heterodetic cyclopeptides that have been isolated from the water extracts of false smut balls on the panicles of rice plants caused by the fungus Ustilaginoidea virens. A concise total synthesis of ustiloxin D has been achieved via an unprecedented ethynyl aziridine ring-opening of phenol derivatives. The longest linear sequence of the synthesis is 15 steps from commercially available compounds.

[reaction: see text] A solid-phase method for the synthesis of tentoxin has been developed. Two key steps-dehydration and N-alkylation-are carried out while the peptide is anchored to the resin. The method, which has been validated by the preparation of a library of tentoxin analogues, should be applicable to the generation of further libraries that have the tentoxin scaffold structure, as well as other structures containing N-alkylated didehydroamino acids.

[reaction: see text] Radical/polar crossover reactions of derivatives of 1-(2-cyclobutenyl)-2-(2-iodoaryl)ethanones with acetone promoted by samarium diiodide and HMPA provide 1-(1-hydroxy-1-methylethyl)-2,2a,4,8b-tetrahydro-1H-cyclobuta[a]naphthalen-3-one derivatives in about 50% isolated yield. This reaction shows promise for construction of the BCD ring fragment of the penitrems.

[reaction: see text] A potential route to the topoisomerase I inhibitor hypoxyxylerone is demonstrated by a highly convergent synthesis of the penta(O-methyl) derivative. The key step in the approach is an anionic homo-Fries rearrangement, little used to date in natural product synthesis and employed here for the first time with a dinaphthalenic substrate, to access the pentacyclic system of hypoxyxylerone.

[reaction: see text] The [3 + 2] annulation reaction of allylsilane 1 with an alpha-keto ester provided the highly substituted tetrahydrofuran 2 as a single diastereomer in high yield. The synthesis of (+/-)-5-epi-citreoviral and (+/-)-citreoviral has been accomplished with this annulation reaction as the key step. Using the pantolactone-derived alpha-keto ester, the allylsilane 1 has been resolved with high enantiomeric purity.

[figure: see text] A phytotoxin, solanapyrone E, has been synthesized from the decalone prepared by the domino Michael reaction of the kinetic enolate of optically pure acetylcyclohexene with methyl crotonate. After several transformations on the decalone ring, condensation of a methyl acetoacetate equivalent installed a pyrone moiety and introduction of a hydroxymethyl unit into the pyrone ring furnished solanapyrone E.

Total synthesis of (+)-sambutoxin has been achieved, establishing the relative and absolute stereochemistry of the naturally occurring mycotoxin. Efforts feature methodology for enantiocontrolled construction of 1,3-anti-dimethyl arrays and a novel Saegusa oxidation to provide a pyridinone methide leading to formation of the central dihydropyran ring.

[reaction: see text] Quinones bearing electron-withdrawing groups can serve as useful precursors to furobenzofuran ring systems through their reaction with 2,3-dihydrofuran. Formal racemic and stereoselective syntheses of the fungal metabolite aflatoxin B(2) are described that utilize this approach to construct the tricyclic ABC-ring core of the molecule.

[reaction: see text] The condensation of allylic diols with unsymmetrical ketones proceeds with high stereoselection to form 2,2-disubstituted 4-acyltetrahydrofurans when the alpha-substituents of the ketone differ substantially in size. A Prins-pinacol condensation of this type is the central strategic step in an enantioselective synthesis of (-)-citreoviral.

[formula: see text] An asymmetric synthesis of (-)-slaframine and N-acetylslaframine has been accomplished starting from an enantiopure dihydropyridone building block. The oxygen-carbon bond at C-1 was incorporated with complete stereoselectivity by using an efficient phenylselenocyclocarbamation reaction.