Nitration versus nitrosation chemistry of menthofuran: remarkable fragmentation and dimerization pathways and expeditious entry into dehydromenthofurolactone |
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Authors: | De Lucia Maria Mainieri Francesco Verotta Luisella Maffei Massimo Panzella Lucia Crescenzi Orlando Napolitano Alessandra Barone Vincenzo Appendino Giovanni d'Ischia Marco |
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Affiliation: | Dipartimento di Chimica Organica e Biochimica, Università di Napoli Federico II, Via Cinthia 4, I-80126 Napoli, Italy. |
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Abstract: | The reaction chemistry of menthofuran (1), a toxic furan terpenoid from various mint oils, with nitric acid and nitrous acid has been investigated. Treatment of 1 with nitric acid afforded a 1:1 mixture of the bisfuran derivatives 5 and 6, resulting from the unexpected cleavage of the furan into two carbonyl fragments (3-methylcyclohexanone and hydroxyacetone) and their subsequent trapping by unreacted 1. Under conditions of high dilution, the nitrofuran derivative 7 was formed instead as the major reaction product. During investigation of this chemistry, it was found that oxidation of 1 with DDQ led to the important fragrant monoterpenoid 4 [dehydromenthofurolactone (anhydro Woodward-Eastman lactone)] in 44% yield. Exposure of 1 to nitrite ions at pH 3 afforded a completely different type of products, encompassing the known lactone 14, the lactam 15, and the remarkable dimer 16, bearing a N-hydroxy-2-pyrrolinone moiety linked to a nitrooximinofuran unit by an oxygen bridge. By using a combined spectroscopic and DFT approach, the constitution and configuration of 16 could be determined. These results fill a gap in the chemistry of furan compounds and describe routes to menthofuran-derived scaffolds of potential synthetic and biomedical relevance. |
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