[3 + 2] Cycloaddition Reactions of 4-Alkyl-3-hydroxy-2H-pyrazolo[4,3-c]iso- quinolinium Inner Salts

• Published in: Journal of organic chemistry Vol. 68; no. 22; pp. 8700 - 8703
• Main Authors: Phillips, Eifion D, Hirst, Simon C, Perry, Matthew W. D, Withnall, Jane
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 31.10.2003; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Organic chemistry; Physical Sciences; Preparations and properties; Science & Technology; BINDING-SITE; SERIES; ANALOGS; BENZODIAZEPINE RECEPTOR LIGANDS; Ester; Anions; Cycloaddition; Nitrogen heterocycle; Iminium compounds; Alcohol; Dipolarophile; Basic medium; Aromatic compound; Tetracyclic compound; Tricyclic compound; Chemical synthesis
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo034160f

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.