Synthesis of cyclopentanoid derivatives via a metal-assisted (3 + 2) cycloaddition reaction

Abstract

The reactions of (n'-allyl)Fp complexes with electron-deficient olefins and acetylenes, and the replacement of the iron complex of the cyclopentyl-Fp complexes thus formed with an organic functionality have been investigated. Cyclic adducts were the exclusive products from the reaction of the simple (n'-allyl)Fp complex (20a) and the (n'-3-methoxyallyl)Fp complex (28) with olefinic species, whereas linear adducts (arising from a H-transfer process), as well as cyclic products, were isolated from the reaction of the (n'-2-methoxyallyl)Fp complex (66) with unsaturated moieties. The reactivity of the 2-methoxyallyl complex was observed to be substantially greater than that of either (20a) or (28). 

Ammonium ceric nitrate oxidation of alcoholic solutions of cyclopentyl-Fp and 2-methoxycyclopentyl-Fp complexes led to the replacement of the Fp group with a carboxylic ester functionality. Similar treatment of 1methoxycyclopentyl-Fp complexes gave a mixture of ketalic and olefinic derivatives. Reaction of cyclopentyl-Fp complexes with gaseous hydrochloric acid afforded products resulting from a ring-opening process, as well as cyclic adducts arising from the replacement of the Fp complex with a proton. Analogous treatment of 2-methoxycyclopentyl-Fp complexes resulted in the elimination of FpOMe to give cyclopentene derivatives. A mixture of brominated and olefinic derivatives were isolated from the reaction of cyclopentyl-Fp complexes with N-bromopyridinium bromide. 

A preliminary study of the possible uses of the metal assisted (3+2) cycloaddition reaction in the synthesis of a variety of cyclopentanoid natural products was also performed.

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