Recent Advances in Solid‐Phase 1,3‐Dipolar Cycloaddition Reactions

Synthesis of Withasomnines and Their Non-natural Analogues from Aldehydes and 4-Nitro-1-butanol in Three Steps

“…Our retrosynthetic analysis suggested that withasomnine 5a could be synthesized from pyrazole 13a via intramolecular alkylation of 13a in which X is a good leaving group (Scheme ). Pyrazole 13a in turn would be accessible via 1,3-dipolar cycloaddition of nitroalkene 11 with a diazoalkane 14 . Nitroalkene 11 would arise from condensation of benzaldehyde 15a with a suitable aliphatic nitro compound 16 .…”

One-Pot, Two-Step Conversion of Aldehydes to Phosphonyl- and Sulfonylpyrazoles Using Bestmann–Ohira Reagent

“…The general methods for the synthesis of pyrazoles are 1,3-dipolar cycloaddition of diazo compounds with alkenes or alkynes (Pechmann synthesis) and the cyclocondensation between hydrazines and 1,3-difunctional compounds (Knorr synthesis) . These approaches were employed for the synthesis of various functionalized phosphonyl- and sulfonylpyrazoles as well. − Recently, we and Smietana et al have employed α-diazo-β-ketophosphonate (Bestmann–Ohira reagent, BOR) 3a as a diazomethyl phosphonate precursor in the 1,3-dipolar cycloaddition with various electron-deficient alkenes (e.g., 2 , Scheme a) for the regioselective synthesis of phosphonylpyrazoles (e.g., 4 ).…”