Bromination and iodination of donor–acceptor cyclopropanes. Evidence for an ET mechanism

✍ Scribed by Vincenzo Piccialli; M.Liliana Graziano; M.Rosaria Iesce; Flavio Cermola

• Book ID: 104252186
• Publisher: Elsevier Science
• Year: 2002
• Tongue: French
• Weight: 188 KB
• Volume: 43
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(02)01966-4

✦ Synopsis

Ethyl 2,2-dimethoxycyclopropanecarboxylates 1a-d react easily with Br 2 and I 2 in CCl 4 or CH 2 Cl 2 leading, in high yields, to 1-ethyl-4-methyl 2-halobutanedioates 2 and 3, respectively. Bromination in the presence of pyridine, NBS, trimethyl phosphate, and iodination with ICl and ICl/pyridine has been also performed. A common SET mechanism may be proposed for both halogenations; depending on the reaction conditions, bromination can also occur via acid-catalysed or S E 2 routes. The reaction of the 2-ethoxyanalogues cis-12 and trans-12 with the same halogens proceeds in a similar manner, giving 3-formyl-2haloesters along with the corresponding diethylacetals as main products. Iodination of 12 with the catalytic system NaI/m-CPBA/ 18-crown-6 has also been investigated.