Synthesis and reactivity of 4-acyl-5-hydroxytriazolines resulting from thermal reaction of aryl and tosyl azides with 2-substituted indane-1,3-diones

Abstract

Reaction of aryl azides 1 with 2-methylindane-1,3-dione 3 in HMPA at 55 °C results in the formation of fairly stable tricyclic 4-acyl-5-hydroxytriazolines 6 in yields greatly decreasing with decreasing electrophilic character of the aryl azide reactant. Similar reaction of 4-nitrophenyl azide 1a with 2-phenylindanedione 4 affords the corresponding 5-hydroxytriazoline 7a in high isolated yield. Upon photolysis or treatment with trifluoroacetic acid the hydroxytriazolines 6 undergo exclusive decomposition to 2-arylamino-2-methylindanediones 12 through the reactive hydroxyaziridine 19 intermediates. On the other hand, upon thermolysis at 95 °C compounds 6 appear to rearrange preferentially to ring-expanded 2-arylisoquinoline-1,3-diones 13, which are believed to result eventually from Wolff rearrangement of initially formed diazo keto amides. The strongly electrophilic tosyl azide 2 reacts smoothly with 2-methylindanedione 3 in HMPA, at room temperature, to give a mixture of the 2-tosylisoquinoline-1,3-dione 14 and the isomeric 1,4-dione 17 to a comparable extent. Under similar conditions, the azide 2 reacts with 2-phenylindanedione 4 to give exclusively the isoquinoline-1,3-dione 15 in virtually quantitative yield. The products 14, 17 and 15 are ascribable to intramolecularly acid-catalysed decomposition of unstable diazocarbonyl compounds resulting from isomerization of reactive 5-hydroxy-1-tosyltriazolines adducts. An X-ray crystal structure analysis of the 4-acyl-5-hydroxytriazoline 6c has been performed.