A Novel Route to a Bromo‐Cyano‐Substituted Azulene and Its Exploitation in the Construction of an Acetylenic Scaffold

Abstract

A novel route to functionalized azulenes is devised from a dihydroazulene precursor. Thus, bromination of 1,1-dicyano-2-phenyl-1,8a-dihydroazulene followed by heating in the presence of bromide ions provides an efficient way to generate 3-bromo-1-cyano-2-phenylazulene. Formation of this somewhat unexpected product was confirmed by X-ray crystallographic analysis. It undergoes a palladium-catalyzed

Dihydroazulene Photoswitches: The First Synthetic Protocol for Functionalizing the Seven‐Membered Ring

“…We have recently reported that bromination of 1 occurs selectively at the 7,8-positions in quantitative yield to provide the dibromide 5 (confirmed by X-ray crystal structure analysis, Figure 1) as a pair of enantiomers. [4] In fact, treatment with two molar equivalents of bromine selectively furnished the tetrabromide 6, while treatment with three (or more) equivalents furnished the hexabromide 7 as confirmed by X-ray crystal structure analysis (Figure 1). Treating dibromide 5 with ca.…”

Gaining Control: Direct Suzuki Arylation of Dihydroazulenes and Tuning of Photo‐ and Thermochromism

“…The synthesis starts with selective bromination of parent unsubstituted DHA 4 to give dibromide 5, [8] followed by elimination of HBr to give the 7-bromo DHA 6.…”

Synthetic protocols for the key functionalizations of the photochromic dihydroazulene scaffold

“…It was instead possible to introduce another bromine in position 7 to give a 3,7-dibromo-substituted DHA through a bromination/elimination protocol, which had already been established for DHA 1 itself (vide infra, Section 4). 31 …”

“…[31][32][33][34] It consists of a sequential bromination/elimination protocol, which furnished selectively the 7-bromo DHA 17 starting from DHA 1 (Scheme 7). Addition of up to three molar equivalents of elemental bromine was possible in the first step (Scheme 8).…”

“…Bromination of 1 occurs selectively at the 7,8-positions in quantitative yield to provide the dibromide 18 as a pair of enantiomers when using only one molar equivalent of bromine. 31 Treatment with two molar equivalents of bromine selectively furnished the tetrabromide 19, while treatment with three (or more) equivalents furnished the hexabromide 20. 32,34 The elimination step to give the 7-bromo DHA 17 from 18 was accomplished in high yield but was successful only upon treatment with lithium hexamethyldisilazide (LiHMDS) at 0 °C; indeed, raising the temperature or using more common bases, such as KOtBu, pyridine, DBU, triethylamine or Hünig's base, gave azulene 21 and other azulene derivatives, and only in few cases, traces of 17.…”