如题。

苯环上的甲氧基脱甲基到羟基，再转化位其他基团。
有人说见过甲氧基一步变溴的反应，如果真可以，那方便多了，溴锂化后可以和很多东西反应。
但是我没见过这类反应，各位高手能提供点信息吗？谢谢啦！

刚才用Scifinder查了一下，没有检索到

^_^ 我也觉得是没有这种反应，不管他了，谢谢niliu！

呵呵，还真没听说过有甲氧基一步变溴的，希望有高手可以来指点一下～～～

应该不可能，因为溴和甲氧基相比，溴是较好的离去基团。
也就是说由溴代一步变为甲氧基是可能的。
明白了吧。

Yeah. He is right!

I know reactions not much. I expect O-Ar bond is a much stronger bond than Br-Ar. How to drive the reaction favorable??

From Org. Chem. textbook, acid can catalyze cleavage C-O bond of ethers.
R-O-R' + excess HX -> RX + R'X +H2O (heat)

However, basicity of the alkoxy group decreased due to pi bonding between O lone-pair and ph. Thus, if it is harder to protonate the alkoxy group to weak the O-Ar. Even, we protonate, then the halide is not as easy to to attack Ph and substitute OR. It is hard for Sn2 Rxn to occur vinyl- and Ph-. It is even hard to give Ph cation (compared to alkyl cation) & ROH!!!
Ph-O-R + HX -> PhOH + RX (in experiment)

If you can convert Ph-OR into Ph-NH2, then you can do Schlemann Rxn to form diazonium. Then you can easily get Ar-X.

Or you can convert Ph-OR into Ph-OTf or PhO2CR, C-O bond should be more easy to be broken.

引用:

原帖由 panda1977 于 2006-6-22 14:29 发表
应该不可能，因为溴和甲氧基相比，溴是较好的离去基团。
也就是说由溴代一步变为甲氧基是可能的。
明白了吧。

[ 本帖最后由 choscar 于 2006-7-7 03:01 编辑 ]

I checked "Comprehensive Organic Transformations by Larock"(703)
PhOH + PPh3 + Br2 -> PhBr (JACS,1964,964 & Org, Syn. Coll. Vol. 1993, 8, 57)

Is this reaction possible for PhOR? I don't know?

As I remember, the BR3 strong Lewis acid (or other metal) can cleavage the ethers. Strong B-O bond (O-M) may compensate a C-O bond broken!??

[ 本帖最后由 choscar 于 2006-7-7 02:53 编辑 ]

Thanks for choscar's suggestion！

I cannot find any literature about Ar-OCH3 to Ar-Br by Scifinder, it seems need two steps. If I have Ar-OH, I would rather change it to Ar-OTf first.

Why you must need one step? Have you checked BBr3 or something like that??

好像BBr3只能脱甲基一般 Ar-OCH3 ——> Ar-OH

其实我是用suzuki反应后得到Ar-OCH3（邻甲氧基苯基硼酸和Ar'-Br反应得到），想将Ar-OCH3转化为Ar-PR2，对Ar-PPh2来说好办，Ar-OCH3 ——> Ar-OH ——> Ar-OTf ——> Ar-PPh2；但是对Ar-PCy2或是Ar-PBu2就不能用这种方法合成了，一般要从Ar-Br或是Ar-Cl过来。主要是老板说他好像见过，要我查查看，那我就得告诉他到底有没有一步就到的反应（就是这个结果），应该是没有 ^_^ （因为原料非常贵）

其实我要得到Ar-Br或是Ar-Cl ：

1。可以从Ar-OH + PPh3 + Br2 ——> Ar-Br得到，反正都做到Ar-OH 这步了 ^_^，就是不知我的底物用这个反应产率如何（分子中还有一些活性大点的亚甲基，怕会取代上溴）。
2。要得到Ar-Cl， 我还可以从前一步的Suzuki反应中来，用邻氯苯基硼酸和Ar'-Br反应得到，就是需要重新摸条件做。