Developments of New Organic Synthetic Reactions Using Inorganic Supports

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In these ten years we have been engaged in the study of development of new synthetic organic reactions with the use of silica gel as a useful catalyst. Another important recent project in our laboratory is electrophilic and nucleophilic substitution reactions at olefinic carbon atoms. The present study was undertaken to combine the both projects and to develop new synthetic methods for the syntheses of various fluorine-containing heterocycles which are otherwise difficultly accessible. The results are as follows. (1) Ethyl vinyl ether was trifluoroacetylated at the beta-position and then converted to allyl beta-trifluoroacetylvinyl ethers by reaction with various allyl alcohols in the presence of silica gel. The products were submitted to Claisen rearrangement with the use of silica gel to yield 3-allyl-1,1,1-trifluoroacetylacetones, from which various fluorine-containing heterocycles were obtained. (2) Various aldehyde hydrazones were successfully trifluoro- acetylated at the azomethine carbons and then converted by novel cyclization to fluorine- containing oxadiazines in the presence of silica gel. From these oxadiazines various fluorine-containing heterocycles such as thiadiazines, imidazoles, pyrazoles, quinoxalines, pyrazines, thiophenes, furans and pyrroles were obtained. (3) 2,4-Bistrifluoroacetyl- 1-dimethylaminonaphthalene was successfully converted with the use of silica gel as catalyst into fluorine-containing [1,2-d][1,3]oxazine.