1.3- Dioxane-4,6-diones arylation

A new, simple, synthesis of 2,4-diaryl-l, 3,5-triazines is shown in Scheme 1. It arose from an attempt to obtain the pyrano[4,3-rf]pyrimidine system by reacting aryl amidines with the 3-methoxymethylenedihydropyran-2,4-dione (1 X= CH2). As well as the desired products, diaryl-I,2,3-triazines were obtained in 30-40% yield. The use of 5-methoxymethylene-2,2-dimethyl-l,3-dioxan-4,6-dione (1 X= 0)(derived from Meldrum s acid) gives the triazines in better yield (> 50%). It was also observed that 3-methoxymethylenefuran-2,4-dione reacted with 5-methylisothiouronium bromide to yield 2,4-bismethylthio-l,3,5-triazine [95M99]. 

The self condensation of a-carbonyl ketenes also constitutes a type (i) synthesis of 2//-pyran-2-oncs. Cyclophanes 627 are synthesized by the thermal decomposition of bis(4,6-dioxo-l,3-dioxanes) 628 and dimerization of the resulting bis(a-carbonyl ketenes) 629 (Scheme 141) <1999JA8270>. Similarly, thermal decomposition of 4,5-diarylfuran-2,3-diones 630 forms the intermediate a-carbonyl ketenes, which dimerize to afford 3,4,5-aryl-2//-pyran-2-ones (Scheme 142) <2003RJ0103>. 

A new purine ring synthesis has been developed.Treatment of the 6-aminopyrimidine (40) with 4-phenyl-1,2,4-triazoline-3,5-dione in dioxan at room temperature provided the adduct (41) in excellent yield. Fusion of (41) with benzaldehyde at 180 C gave 8-phenyltheophylline (42). A number of 8-aryl analogues were prepared by this method. 

Derivatives of 2,2-dimethyl-l,3-dioxan-4,6-dione (Meldrum s acid) and the sodium salts of substituted malonic esters undergo electrophilic C-arylation in high yield with aryllead triacetates this provides a useful route to a-arylalkanoic acids, compounds of interest in the pharmaceutical industry and as synthetic intermediates (Scheme 13.8) [36]. 

Although azide reagents have been utilized in a number of chemical transformations, to date PS-TsA has only been utilized for the direct transfer of a diazo function to methylene groups flanked by either two carbonyls (eq 2), a carbonyl and an aryl sulfonyl (eq 3), or the methylene of lO/ anthracen-9-one. Diazodicarbonyl compounds such as 5-diazo-2,2-dimethyl-[l,3]dioxane-4,6-dione, 2-diazo-3-oxo-butyric acid ethyl ester, lO-diazo-lO/ anthracen-9-one, 2-diazo malonic acid diethyl ester, and 2-diazo-3-oxo-butyric acid ter/-butyl ester, as well as... 

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