[3 + 2] cycloaddition reactions of 4-alkyl-3-hydroxy-2H-pyrazolo[4,3-c]isoquinolinium inner salts.
Heating dipolarophiles with 4-alkyl-3-hydroxy-2H-pyrazolo[4,3-c]isoquinolinium hydroxide inner salts results in [3 + 2] cycloaddition across positions 3a and 5 of the aromatic system to give the [3 + 2] cycloadducts in good yield. When the 4-alkyl substituent is a 2-acetate ester and the methylene group can be deprotonated, a second mode of [3 + 2] cycloaddition becomes available for the resulting anion (across the side chain methine group and position 5 of the aromatic system) and occurs under basic conditions, allowing either of two modes of [3 + 2] cycloaddition to be selected by appropriate choice of reaction conditions.
Phillips
Eifion D
ED
Department of Medicinal Chemistry, AstraZeneca R&D Charnwood, Bakewell Road, Loughborough, Leicestershire LE11 5RH, United Kingdom. eifion.phillips@astrazeneca.com
Hirst
Simon C
SC
Perry
Matthew W D
MW
Withnall
Jane
J