Attempted Synthesis of the Dithiophene Analogs of Biphenylene

Abstract

Synthesis o f the four possible dithiophene analogs o f biphenylene ( ), viz., cyc 1 obuta 11.2-b : 3.4-d ' Jdi t h i ophene ( ) , cyc 1 obu t a [ 1.2.41 : 3.4-b ' I-di f.h 1 op I e n e m . cyclobuta[1,2-6:3.4-~ p i t h i o p h e n e t). and cyclobuta-n,2-~?J,4-~ jdithiophe;e (&) has been explored Fsing several d i f f e r e n t approaches. cessful s i m i l a r l y as the former e f f o r t s o f k W e and Mynberg. t h e attcnpts t o obtain the i r o n t r i c a r b o n y l complexes of these w o u n d s M c h were thought t o be m r e stable. i n d i c a t e t h a t these four conpounds w i l l be highly unstable. also i n view o f t h e considerable r i n g strain. A l l these attenpts have been unsuc-The m0 calculations c a r r i e d out f o r cyclobutadithiophenes Equally msuccessful were I NTROOUCTION Biphenylene (i), with a central f o u r m e r e d cyclobutadiene ring. i s m e o f the nonclassical aromatic hydrocarbons i n which the cyclobutadiene system I s s t a b i l i z e d by t h e presence o f two fused benzene rings.'" Thus, r h i l e cyclobutadiene e x i s t s o n l y i n t h e form o f i t s w-conplexes w i t h t r a n s i t i o n m t a l s (cyclobutadieneiron t r i c a r b o n y l can serve as a t y p i c a l e~a n p l c ) .~" biphenylene i s a stable conpound. K e k u l i structures undoubtedly contribute t o I t s s t a b i l i t y . Because of i t s unusual and i n t e r e s t i n g s t r u c t u r e and o f t e n contradictory r e s u l t s obtained w i t h d i f f e r e n t types of quantum-chemical calculations. chemical and physical properties o f biphenylene have been extensively studied and reviewed.'-1o

Theoretical Study on the Structures, Electronic Properties, and Aromaticity of Thiophene Analogues of Anti-Kekulene

“…In this context, we herein report a theoretical study on the thiophene analogues of cyclic [n]phenylenes 1-4, where all thiophene rings are fused to 4MRs at the b-position, in which we investigate their geometries and aromaticity based on DFT calculations (Figure 1e). Together with 1-4, as reference compounds we investigated the geometries and aromaticity of four cyclobutadithiophenes (CDTs; Figure 1f) [66,67], cyclobuta[1,2b:4,3-b ]dithiophene (syn-bbCDT) and its regioisomer (anti-bbCDT), cyclobuta[1,2-b:3,4c ]dithiophene (bcCDT), and cyclobuta[1,2-c:3,4-c ]dithiophene (ccCDT), as well as antikekulene. In syn-bbCDT, which is the simplest substructure of 1-4, the aromaticity and anti-aromaticity of the TRs and 4MR were preserved.…”