5- alkylidene-l,3-dioxane-4,6-dione

The reaction of nucleophiles with 1,3-dioxanes containing three double bonds is mainly confined to the group of 5-alkylidene-l,3-dioxane-4,6-diones. The parent compound, 5-methylene-l,3-dioxane-4,6-dione, is, however, quite unstable. Two reagents 170 and 171 have been developed to prepare 5-methylene-l,3-dioxane-4,6-dione in situ (Figure 8) <19968215, 2002SC2009>. 

Addition of various nucleophiles to the o o-double bond of 5-alkylidene-l,3-dioxane-4,6-diones has been reported in the literature. Two different pathways have been examined (1) the addition of a nucleophile followed by aqueous (protic) workup and (2) the transition metal-catalyzed successive addition of a nucleophile and an electrophile to the double bond (Scheme 16). 

Phenols are also suitable nucleophiles for 5-alkylidene-l,3-dioxane-4,6-diones, when activated by Yb(OTf)3. Depending on the substitution pattern at C-1, several useful coumarins, dihydrocoumarins, 4-chromanones, and chromones were obtained (Scheme 21) <2006JOC409>. 

Reactions of carbon suboxide with oxo compounds 5-Alkylidene-l,3-dioxane-4,6-diones from aldehydes Furans from y-diketones... 

Tsuno, T, Sugiyama, K. and Ago, H., A facile epoxidation of 5-methylene-l,3-dioxane-4,6-diones with hydrogen peroxide without catalyst. Heterocycles, 38, 2631-2654, 1994 Tsuno, T. and Sugiyama, K., Addition reaction of photoenols from o-methyl-substituted aromatic ketones with 5-alkylidene-l,3-dioxane-4,6-dione derivatives. Heterocycles, 38, 859-876, 1994 Tsuno, T. and Sugiyama, K., Diels-Alder reaction of photoenol of 2-methylbenzaldehyde with 5-alkylidene-l,3-dioxane-4,6-dione derivatives, iTeterocyc/es, 32,1989-2004, 1991. 

As in many other areas of 1,3-oxazine chemistry, ketenes and isocyanates generated in situ are often used to prepare oxazin-6-ones. For example, 2,4-disubstituted l,3-oxazin-6-ones (135) are readily available through the thermolysis of 5-[(A-acylamino)alkylidene]-l,3-dioxane-4,6-diones (134). The latter are generated from the reactions of the appropriate ethyl acylimidate (133) and Meldrum s acid (Scheme 36) <86CPB1980>. Similarly, the bismethylthiomethylene derivative (136) reacts with benzamides in the presence of potassium hydroxide to afford the methyl-thioacylaminomethylene derivatives (137 R = MeS), which can be reacted further with ammonia to give the amino compounds (137 R = NHj). In turn, these products can be thermolyzed to afford the oxazinones (138 R = MeS) or (138 R = NH2), respectively (Scheme 37) <91SC1213>. 

Tsuno, T and Sugiyama, K., Allenyl(vinyl)methane photochemistry. Photochemistry of 5-[2-(l,2-propadienyl)-substituted alkylidene]-2,2-dimethyl-l,3-dioxane-4,6-diones. Bull. Chem. Soc. Jpn., 68, 3175-3188, 1995. 

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