Iron complex-catalyzed N-arylation of pyrazoles under aqueous medium
作者:Hang Wai Lee、Albert S.C. Chan、Fuk Yee Kwong
DOI:10.1016/j.tetlet.2009.08.018
日期:2009.10
diamine ligand is a highly effective catalyst for N-arylation of pyrazoles using aryl and heteroaryl iodides. It is notable to show that this complex is tolerable under aqueous medium and particularly the whole reaction utilizes water as the sole solvent without any additional organic co-solvents and surfactants. Attempted study using other nitrogennucleophiles is described. This newly developed system provides
The present invention provides a compound having an excellent inhibitory action on melanin production and being useful as a whitening agent, and a skin external preparation containing the compound. The whitening agent of the present invention comprises, as an active ingredient, a compound represented by formula (1) or a pharmacologically acceptable salt thereof:
wherein X
1
, X
2
, and X
3
are each CR
2
or N; R
1
, R
2
, and R
3
are each H, C
1-6
alkyl, C
1-6
alkoxy, SH, OH, or NR
b
R
c
, wherein R
b
and R
c
are each H, C
1-6
alkyl, or hydroxy-C
1-6
alkyl, or NR
b
R
c
forms a saturated or unsaturated 5- or 6-membered hetero ring; and B is a substituted or unsubstituted pyrazole, imidazole, pyridine, or piperidine; with the proviso that at least one of R
1
, R
3
, R
4
, and R
6
is a group other than C
1-3
alkyl in the case where X
1
═X
2
═Y
1
═N and X
3
═CR
2
.