James H. Rigby

Total synthesis of (±)-α-lycorane and 4,5-dehydroanhydrolycorine

Abstract The total syntheses of (±)-α-lycorane and dehydroanhydrolycorine are described. The key intermediate in both approaches is the hydroindolone 5 , prepared from the [1+4] cycloaddition reaction of 1-isocyanatocyclohexene and cyclohexyl isocyanide. Alkylation of 5 with arylbromide 6 afforded 7 . Hydrolysis of enamide 7 followed by reduction of the resultant enol yielded 10 as a single diastereomer. Radical-based cyclization of this intermediate gave 11 possessing the requisite trans -fusion between rings B and C in good yield. Radical deoxygenation followed by reduction of the amide carbonyl function afforded (±)-α-lycorane. Similarly, alkylation of 5 with 6-(chloromethyl)-5-iodo-1,3-benzodioxole gave 14 . Treatment of 14 with Pd(OAc) 2 employing the Jeffery modification of the Heck reaction gave tetracycle 9 . Hydrolysis of 9 followed by oxidation with DDQ afforded 15 . Reduction of the two carbonyl functions in this material using lithium aluminum hydride afforded 4-hydroxyanhydrolycorine ( 16 ). Mesylation of the hydroxyl group led to rapid, spontaneous elimination producing anhydrodehydrolycorine.

Removal of methoxyethoxymethyl ethers with trimethylsilyl chloride-sodium iodide

Abstract Trimethylsilyl chloride-sodium iodide has been used for the mild removal of methoxyethoxymethyl ethers.

SYNTHETIC STUDIES ON THE ERYTHRINA ALKALOIDS. PREPARATION OF ()-2-EPI-ERYTHRINITOL

Abstract The erythrina alkaloid, 1,3,4,6-tetrahydro-3,15,16-trimethoxyerythrinan-2-ol (2-epi-erythrinitol), has been synthesized by a sequence featuring a [1+4] vinyl isocyanate-isocyanide cycloaddition followed by an intramolecular Heck reaction for assembly of the erythrinan ring system.

Chromium(0) promoted [6π+2π] cycloaddition reactions

Abstract The chromium(0) mediated [6+2] cycloaddition reactions of a variety of cyclic trienes with substituted alkenes is detailed. The reactions can be effected either photochemically or thermally. Reactions promoted with catalytic quantities of chromium(0) are also described.

Tricarbonyl(tropone)iron as a useful functionalized enone equivalent

Abstract Tricarbonyl(tropone)iron has been shown to undergo reactions that are characteristic of an isolated enone.

Construction of the ingenane core using an Fe(III) or Ti(IV) Lewis acid-catalyzed intramolecular [6+4] cycloaddition

A facile entry into the ingenane core using a Lewis acid-catalyzed intramolecular [6+4] cycloaddition has been developed. Ti(IV)- and Fe(III)-based Lewis acids were found to mediate the higher order cycloaddition in good to excellent yield at room temperature. Chiral Ti(IV) Lewis acids were found to induce modest asymmetry in the resultant [6+4] cycloadducts.

Metal promoted higher-order cycloaddition reactions. A facile entry into substituted eight- and ten-membered carbocycles.

Abstract Substituted eight- and ten-membered carbocycles can be accessed by employing a metal promoted higher-order cycloaddition of heterocyclic trienes followed by heteroatom extrusion.

Bis(alkylthio)carbenes as Novel Reagents for Organic Synthesis

Abstract Bis(alkylthio)carbenes have been shown to be a useful class of reactive intermediates for applications to organic synthesis. Substituted hydroindolones, isatins and hydroquinolones can be prepared by the addition of these carbenes to vinyl isocyanates.

Carbamoyl radicals from Se-phenylselenocarbamates: Intramolecular additions to alkenes

Abstract A series of 5 exo -trig cyclizations of carbamoyl radicals generated from readily available Se-phenylselenocarbamates is reported. Kinetic studies indicate that the rate constant of this cyclization exceeds 1×10 8 s −1 in reveral cases.

Room temperature chromium(0)-catalyzed higher-order cycloaddition reactions

Abstract Room temperature thermal and photochemical chromium(0)-catalyzed higher-order cycloaddition processes are described. A novel photoactivated reaction employing a substoichiometric amount of a chromium(0) pre-catalyst has also been demonstrated in a multi-component [6π+2π+2π] cycloaddition. These chromium-mediated cycloaddition reactions can also be conducted in aqueous media.