Regioselective Haloaromatization of 1,2-Bis(ethynyl)benzene via Halogen Acids and PtCl<sub>2</sub>. Platinum-Catalyzed 6-π Electrocyclization of 1,2-Bis(1‘-haloethenyl)benzene Intermediates
作者:Ching-Yu Lo、Manyam Praveen Kumar、Hsu-Kai Chang、Shie-Fu Lush、Rai-Shung Liu
DOI:10.1021/jo0518295
日期:2005.12.1
Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100105 degrees C, 2 h) afforded 1,2-bis(1'-baloethenyl)benzene species 2-Br and 2-I in 98% and 95% yields, respectively. The hydrochlorination of endiyne 1 failed to proceed at elevated temperature but was implemented efficiently by PtCl2 (5 mol %) in hot 3-pentanone (100 degrees C, 2 h) to give 1,2-bis(1'-chloroethenyl)benzene 2-Cl in 80% yield. In the presence of PtCl2 (5 mol %), these halides 2-Cl, 2-Br, and 2-I were subsequently converted to 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in the mother solution via sequential 6-pi electrocyclization and dehalogenation reactions. PtCl2 (5 mol %) also effected direct haloaromatization of endiyne 1 with HX (X = Cl, Br, 1) and gave 1-halonaphthalenes 3-Cl, 3-Br, and 3-I in 64-71% yields. This investigation reports the scope and the regioselectivity of haloaromatization of various enediynes catalyzed by PtCl2.