Regioselective haloaromatization of 1,2-bis(ethynyl)benzene via halogen acids and PtCl2. Platinum-catalyzed 6-pi electrocyclization of 1,2-bis(1'-haloethenyl)benzene intermediates.
[reaction: see text] Treatment of 1,2-bis(ethynyl)benzene (1) with aqueous HX (X = Br, I) in hot 3-pentanone (100-105 degrees C, 2 h) afforded 1,2-bis(1'-haloethenyl)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, I) 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.
Lo
Ching-Yu
CY
Department of Chemistry, National Tsing-Hua University, Hsinchu, Taiwan 30043, ROC.
Kumar
Manyam Praveen
MP
Chang
Hsu-Kai
HK
Lush
Shie-Fu
SF
Liu
Rai-Shung
RS
D001555:Benzene Derivatives / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D006846:Hydrocarbons, Halogenated / Q000138:chemical synthesis*; D010984:Platinum; D011084:Polycyclic Aromatic Hydrocarbons / Q000138:chemical synthesis*
D001555:Benzene Derivatives; D006846:Hydrocarbons, Halogenated; D011084:Polycyclic Aromatic Hydrocarbons; D010984:Platinum