RESUMO
Iodo- or 2-bromopyridine N-oxides were readily magnesiated with i-PrMgCl x LiCl via the iodine or bromine-magnesium exchange. The bromine adjacent to pyridine N-oxide (at the 2- or 6-position) can be regioselectively magnesiated in the presence of other position substituted halogens. This method was tested in various substituted pyridine N-oxide systems, and has been successfully applied to the total synthesis of caerulomycins E and A.
RESUMO
A novel two-step synthesis of 2-arylbenzofurans has been developed. It involves a selective cross McMurry coupling of a salicylaldehyde or substituted salicylaldehyde with an aromatic aldehyde and a sequential oxidative cyclization of the resulting ortho-vinylphenols. Utilizing this synthetic protocol, a variety of 2-arylbenzofurans including cicerfuran have been efficiently synthesized.
Assuntos
Benzofuranos/síntese química , Aldeídos/química , Benzofuranos/química , Ciclização , Estrutura Molecular , Oxirredução , EstereoisomerismoRESUMO
The selective cross McMurry couplings of diaryl or aryl ketones with various substituted ketones were achieved in 53-94% isolated yields. It is believed that the strong affinity of the substituents to the low-valent titanium surface plays an important role in regards to moderating selectivity. Through the introduction of such substituents followed by their removal post McMurry coupling, structurally similar ketones can be effectively cross-coupled.