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Cyclization of 1,4‐Phenylenediacrylic Acid with Thionyl Chloride and Subsequent Suzuki–Miyaura Reactions Revisited. The Products are Benzo[1,2‐ b ;5,6‐ b ′]dithiophenes and not Benzo[1,2‐ b ;4,5‐ b ′]dithiophenes
Author(s) -
Hassan Zahid,
Reimann Sebastian,
Wittler Kai,
Ludwig Ralf,
Villinger Alexander,
Langer Peter
Publication year - 2012
Publication title -
advanced synthesis and catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.541
H-Index - 155
eISSN - 1615-4169
pISSN - 1615-4150
DOI - 10.1002/adsc.201100668
Subject(s) - chemistry , thionyl chloride , molecule , aryl , quantum chemical , coupling reaction , crystal structure , stereochemistry , chloride , medicinal chemistry , catalysis , organic chemistry , alkyl
The reaction of 1,4‐phenylenediacrylic acid with thionyl chloride was reinvestigated. In earlier reports [ Liebigs Ann. Chem. 1980 , 1172; Heterocycles 1995 , 41 , 2691; Adv. Synth. Catal. 2009 , 351 , 2683] it was claimed that 3,7‐dichlorobenzo[1,2‐ b ;4,5‐ b ′]dithiophenes were formed in these reactions. Herein, we provide unambiguous evidence that the assignment of these structures is wrong and that, in contrast, 3,6‐dichlorobenzo[1,2‐ b ;5,6‐ b ′]dithiophenes are formed. As a consequence, the structures of these parent molecules and of numerous aryl‐substituted derivatives prepared by Pd‐catalyzed cross‐coupling reactions have to be revised. As many of these dithiophenes were reported to show interesting optical, thermal and electronic properties, the theoretical explanations for these properties have to be reconsidered in the light of the corrected structures reported herein. Our structural assignments are based on X‐ray crystal structure analyses of the parent molecules and on NMR spectroscopic studies of the first unsymmetrical derivatives. Besides, mechanistic investigations based on quantum chemical calculations have been carried out which support the formation of the 3,6‐dichlorobenzo[1,2‐ b ;5,6‐ b ′]dithiophene isomers.