A Simple and Environmentally Benign Method for the Synthesis of Naphthoxazin-3-one Derivatives

Carbamatoalkylnaphthol derivatives have been synthesized in good yields in a one-pot, and efficient process by condensation of β-naphtol, aromatic aldehydes and methyl carbamate in ionic liquid media.Ring closure of carbamatoalkylnaphthol derivatives occurred in ionic liquid media at 160 o C to give 1,2-dihydro-1-arylnaphtho[1,2-e][1,3]oxazin-3-one derivatives.Aromatic-condensed oxazinone derivatives are a very important class of heterocyclic compounds since many of this heterocyclic system exhibit biological activities. 1 For example, naphthalene-condensed 1,3-oxazin-3-ones have been reported as anti-bacterial agents. 2 This class has also been used as precursors in the preparation of phosphinic ligands for asymmetric catalysis. 3However, to the best of our knowledge, there was only very few reports of the synthesis of naphthalene-condensed oxazinone derivatives in the literature. 2,4Recently, Fulop and co-workers, disclosed that the condensation of amino alkylnaphthols as precursors with phosgene in the presence of Et 3 N, gave naphthalene-condensed 1,3-oxazin-3-one derivatives in moderate yields. 5Cimarelli et al. used carbonyl diimidazole instead of phosgene. 6All methods have used either expensive, toxic and hazardous reagents and solvents or starting material such as amino alkylnaphthol which was prepared in a multi-step reaction using harsh reaction conditions. 7 Therefore, the discovery of new, simple and green methods for synthesis of naphthoxazinone derivatives is of prime importance.Carbamates have attracted considerable interest in the recent years.Its derivatives widely used as intermediate for the synthesis of pesticides, herbicides and medical drugs. 8Furthermore, carbamates are found as protecting groups for the amino function, especially in the chemistry of peptides and peptidomimetics. 9Initially these compounds were almost prepared from phosgene, 10a phosgene derivatives 10b or isocyanates 10c in reaction with alcohols.This procedure had several drawbacks, among which the extreme toxicity of phosgene and generation of by-products.The past few years have witnessed a growing interest in ionic liquids as solvent systems for organic