On the Reaction of 1-Aza-2-azoniaallene Salts with Acetylenes

✍ Scribed by Wang, Quanrui ;Al-Talib, Mahmoud ;Jochims, Johannes C.

• Publisher: Wiley (John Wiley & Sons)
• Year: 1994
• Tongue: English
• Weight: 732 KB
• Volume: 127
• Category: Article
• ISSN: 0009-2940
• DOI: 10.1002/cber.19941270313

✦ Synopsis

Abstract

1‐Aza‐2‐azoniaallene cations 3, prepared in situ from geminal chloro(alkylazo) compounds 2, react with acetylenes 4 to give either 1__H__‐pyrazolium salts 6 or 4__H__‐pyrazolium salts 7 or mixtures of both. 4__H__‐Pyrazolium salts with a hydrogen atom attached to C(4) rearrange to the protonated 1__H__‐pyrazoles 8, from which the free bases 9 are obtained upon treatment with aqueous NaOH. According to AM1 calculations the cycloaddition of acetylenes to 1‐aza‐2‐azoniaallene cations is a concerted process, which can be classified as a “1,3‐dipolar cycloaddition with reverse electron demand”. The cycloaddition forming the intermediates 5 is followed by an [1,2] alkyl shift to furnish the final products 6–8. The direction of the [1,2] shift has been found to be governed by subtle steric effects.