Adição de organometálicos a orto e paranaftoquinonas

Abstract

The objective of this work is the study of methylation, benzylation, allylation and propargylation reactions of ortho and para-naphthoquinones, derived from lapachol (2-methoxylapachol (2), ß-lapachone (3), a-lapachone (4) and a-xyloidone (5)) using organometallic reagents of magnesium, indium and tin. The initial reactions, with Grignard reagents (methyl-magnesium iodide, benzyl-magnesium chloride and allylmagnesium bromide), indicate that there is regioselectivity in the process, since the addition occurs, in most cases, at only one of the carbonyls, even when there is unused reagent after the reaction time. It is possible that coordination of the Grignard reagent by the oxygen of the pyran ring has an influence in the formation of the products. The reactions were not very clean, and formation of many by-products always occurred, with exception of reactions with ß-lapachone (3). Allylation and propargylation reactions were carried in aqueous solvent (Barbier-type reactions), using indium and tin as metals. In the reactions with tin, it was necessary to use an ultrasonic bath to force dissolution of the metal and start to the reaction. The best results resulted from the use of allyl-indium, because, in some cases, use of allyl-tin led to the destruction of part of the naphthoquinone reagent. The same selectivity seen previously with the Grignard reagents, was also observed in these reactions, but the yields, in this in case, were always superior, since there were not so many by-products. A great advantage in the use of the metal indium, beside the good yields, comes from reaction rates, much faster than those for tin. The propargylation with tin was not successful with a-lapachone (4) and 2-methoxylapachol (2), (there was practically no product formation), and with ß- lapachone there was only had a modest yield. With propargyl-indium the results were more inspiring, leading in some cases to formation of both allene and acetylene products.