Regioselective 2-acylation of N-substituted pyrroles by intramolecular delivery

✍ Scribed by Charles W. Jefford; Qian Tang; John Boukouvalas

• Book ID: 104226511
• Publisher: Elsevier Science
• Year: 1990
• Tongue: French
• Weight: 205 KB
• Volume: 31
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)94412-5

✦ Synopsis

Agsslract. N-substituted pyrroles prepared from o-amino acids are converted to their mixed anhydrides by treatment with an acid chloride and base. Subsequent treatment with AlCls brings about rearrangement to the corresponding 2-acyl derivatives in overall yields of 55-S]%.

The regioselectivity of attack by electrophilic reagents on pyrroles depends crucially on the character of the substituents.' In general, attack on pyrrole itself takes place preferentially at the C2 position.' However, progressive diversion to C3 occurs with increasing bulk of the N-substituent.s In fact, this tendency has been exploited for synthesizing 3-substituted pyrroles.' We now show that such a proximity effect can be turned to advantage when the reagent forms part of the group attached to the N-atom. We trophile 1 could be induced to undergo intramolecuhu transfer to give the dipolar intermediate 2 (Scheme 1).