Donor-acceptor diazocarbonyl carbenes, derived from aryldiazoacetates, are important reagents for a wide variety of metal-catalyzed transformations owing to their ability to impart high levels of site-selectivity, diasteroselectivity, and enantioselectivity. A major limitation of this chemistry, however, lies in the nature of the donor group being primarily restricted to aryl groups. To date, there has been only one successful synthesis of an amino donor group diazocarbonyl compound, which was obtained by using 4-phthalimido-N-methanesulfonyl-1,2,3-triazole as a surrogate and investigated initially in thermal aminocyclopropanation reactions. Herein we describe the thermal intermolecular [3+2] cycloaddition reaction of 4-phthalimido-N-sulfonyl-1,2,3-triazoles with a range of mono- and di-substituted arenes to give cycloadducts in moderate to good yields. Interestingly the [3+2] cycloaddition reaction takes place across the more substituted arene C–C double bond to give 5,7a-substituted dialkyldihydroindoles products from disubsituted arenes. For monosubstituted arenes, a mixture of the 6-alkyl and 7a-alkyl substituted dihydroindoles are formed. For both cases, the fully aromatized diaminosytrenes were obtained as a minor byproduct and were shown to arise from thermal ring opening of the alkyldihydroindoles. Finally, we show that the 6-substitued dihydroindole products can be oxidized to valuable 3-aminoindoles containing 6-subsitution. This study extends the utility of 4-phtalimido-N-methanesulfonyl-1,2-3-triazoles and sets the stage for understanding the nature of the free aminocarbenes.

Thermal intermolecular [3+2] cycloaddition reactions of 4-phthalimido-N-sulfonyltriazoles and substituted arenes

253rd National Meeting (2017)

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