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New Results in Homoheptalene Chemistry
Author(s) -
Rüedi Georg,
Hansen HansJürgen
Publication year - 2001
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/1522-2675(20010516)84:5<1017::aid-hlca1017>3.0.co;2-l
Subject(s) - chemistry , yield (engineering) , dimethyl acetylenedicarboxylate , formylation , bicyclic molecule , double bond , methylamine , structural isomer , column chromatography , medicinal chemistry , stereochemistry , organic chemistry , cycloaddition , catalysis , materials science , metallurgy
The thermal reaction of homoazulene (=bicyclo[5.3.1]undeca‐1,3,5,7,9‐pentaene; 2 ) with dimethyl acetylenedicarboxylate (ADM) in 1,2‐dichloroethane (ClCH 2 CH 2 Cl) results, in contrast to an earlier report [5], in formation of not only dimethyl homoheptalene‐4,5‐dicarboxylate (=bicyclo[5.5.1]trideca‐1,3,5,7,9,11‐hexaene‐4,5‐dicarboxylate; 3 ), but also of a 4 : 1 mixture of 3 and dimethyl homoheptalene‐2,3‐dicarboxylate ( 13 ) in almost quantitative yield ( Schemes 1 and 3 ). The structures of both homoheptalenes have been corroborated by X‐ray crystal‐structure analysis ( Fig. 5 ). The double‐bond‐shifted (DBS) isomers 3 ′ and 13 ′ of 3 and 13 , respectively, could not be detected in their 1 H‐NMR spectra (600 MHz threshold of detection ≥0.5%), in agreement with the AM1‐calculated ΔH values of the four isomeric homoheptalene‐dicarboxylates ( cf. Table 4 ). Vilsmeyer formylation of homoazulene ( 2 ) gave homoazulene‐8‐carbaldehyde ( 14 ) in a yield of 67%, which, on treatment with benzylidene‐(triphenyl)‐ λ 5 ‐phosphane, gave, in almost quantitative yield, a 1.6 : 1 mixture of ( Z )‐ and ( E )‐8‐styrylhomoazulene (( Z )‐ 15 and ( E )‐ 15 , resp.). Thermal reaction of the latter mixture with ADM in 1,2‐dichloroethane led, in a yield of 42%, to a 5 : 1 mixture of dimethyl ( Z )‐ and ( E )‐2‐styrylhomoheptalene‐4,5‐dicarboxylate (( Z )‐ 15 and ( E )‐ 16 , resp.). Both isomers were separated by column chromatography on silica gel. Again, the DBS isomers of ( Z )‐ 16 and ( E )‐ 16 , i.e. , ( Z )‐ 16 ′ and ( E )‐ 16 ′, could not be detected in the 1 H‐NMR spectra (600 MHz) of pure ( Z )‐ 16 and ( E )‐ 16 .