DTBB-catalysed lithiation of 6-chloro-1-hexene and related systems: synthetically useful temperature-dependent behaviour

✍ Scribed by Miguel Yus; Rosa Ortiz; Fernando F Huerta

• Book ID: 104250838
• Publisher: Elsevier Science
• Year: 2002
• Tongue: French
• Weight: 77 KB
• Volume: 43
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(02)00415-x

✦ Synopsis

The reaction of 6-chloro-1-hexene 1 with lithium powder and a catalytic amount of 4,4%-di-tert-butylbiphenyl (DTBB, 5% molar) in THF at -78°C gives the corresponding organolithium intermediate 2, which by reaction with different electrophiles [Bu t CHO, PhCHO, Et 2 CO, (CH 2 ) 5 CO, PhCOMe] affords, after hydrolysis with water, the expected products 3. The same reaction performed at -30°C gives cyclopentyl derivatives 5, probably by cyclisation of the open-chain intermediate 2 to give the cyclic organolithium compound 4. For the tertiary derivative 6, only the cyclic compound 10 could be isolated at -30°C due to the great instability of the corresponding tertiary organolithium intermediate 7, which undergoes a proton abstraction even at -78°C. From allyl 2-chloro-phenyl ether 11 only the corresponding cyclic compound 14 was isolated either at -78°C or at -30°C. In all cases a carbanionic cyclisation, better than a radical one, is postulated to occur.