Fusicoccin Synthesis by Intramolecular [4+4] Photocycloaddition of 2-Pyridones: Stereocontrol of the Cycloaddition and Elaboration of the Pentacyclic Product

Autor:	Kevin F. McGee, Scott McN. Sieburth, Taleb H. Al-Tel
Rok vydání:	2004
Předmět:	chemistry.chemical_compound chemistry Fusicoccin Stereochemistry Amide Intramolecular force Organic Chemistry Stereoselectivity Solvent effects Catalysis Cycloaddition Cope rearrangement Stereocenter
Zdroj:	Synthesis. 112:1185-1196
ISSN:	1437-210X 0039-7881
Popis:	Intramolecular photocycloaddition of a three-carbon tethered pyrindinone–pyridone system yields the 5-8-5 ring system of the fusicoccin/ophiobolin/ceroplastol families. The stereoselectivity of the cycloaddition was found to be dependent on nitrogen substitution; N-methylation led to exclusively trans products while an absence of nitrogen substitution resulted in solvent-dependent stereoselectivity. Solvent and concentration effects for this cycloaddition were consistent with a hydrogen-bonded dimer that enforces a pro-cis conformation in nonpolar solvents and at higher concentrations. The cis-isomer, a fusicoccin synthesis intermediate, underwent a Cope rearrangement at ambient temperature but could be trapped efficiently as the mono epoxide, yielding a product with six new stereogenic centers. A four-step transformation of an amide carbonyl to a methyl group was achieved using a carbamoyl group to activate the amide for cleavage.
Databáze:	OpenAIRE
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