Chen, Yi;
Kunz, Roland W.;
Uebelhart, Peter;
Weber, Roland H.;
Hansen, Hans‐JüRgen
Thermal Reaction of Highly Alkylated Azulenes with Dimethyl Acetylenedicarboxylate: HOMO(Azulene) vs. SHOMO(Azulene) Control in the Primary Thermal Addition Step
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Media type:
E-Article
Title:
Thermal Reaction of Highly Alkylated Azulenes with Dimethyl Acetylenedicarboxylate: HOMO(Azulene) vs. SHOMO(Azulene) Control in the Primary Thermal Addition Step
Contributor:
Chen, Yi;
Kunz, Roland W.;
Uebelhart, Peter;
Weber, Roland H.;
Hansen, Hans‐JüRgen
Description:
<jats:title>Abstract</jats:title><jats:p>The reaction of highly alkylated azulenes with dimethyl acetylenedicarboxylate (ADM) in decalin or tetralin at 180–200° yields, beside the expected heptalene‐ and azulene‐1,2‐dicarboxylates, tetracyclic compounds of type <jats:italic>‘anti’</jats:italic>‐<jats:bold>V</jats:bold> and tricyclic compounds of type <jats:bold>E</jats:bold> (<jats:italic>cf. Schemes 2–4</jats:italic> and <jats:italic>8–11</jats:italic>). The compounds of type ‘<jats:italic>anti</jats:italic>’‐<jats:bold>V</jats:bold> represent <jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> adducts of the primary tricyclic intermediates <jats:bold>A</jats:bold> with ADM. In some cases, the tricyclic compounds of type <jats:bold>E</jats:bold> also underwent a consecutive <jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> reaction with ADM to yield the tetracyclic compounds of type ‘<jats:italic>anti</jats:italic>’‐ or ‘<jats:italic>syn</jats:italic>’‐<jats:bold>VI</jats:bold> (<jats:italic>cf. Schemes</jats:italic> 2 and <jats:italic>8–11</jats:italic>). The tricyclic compounds of type <jats:bold>E</jats:bold>, namely <jats:bold>4</jats:bold> and <jats:bold>8</jats:bold>, reversibly rearrange <jats:italic>via</jats:italic> [1,5]‐C shifts to isomeric tricyclic structures (<jats:italic>cf</jats:italic>. <jats:bold>18</jats:bold> and <jats:bold>19</jats:bold>, respectively, in <jats:italic>Scheme 6</jats:italic>) already at temperatures > 50°. Photochemically <jats:bold>4</jats:bold> rearranges to a corresponding tetracyclic compound <jats:bold>20</jats:bold> <jats:italic>via</jats:italic> a di‐π‐methane reaction. The observed heptalene‐ and azulene‐1,2‐dicarboxylates as well as the tetracyclic compounds of type ‘<jats:italic>anti</jats:italic>’'‐<jats:bold>V</jats:bold> are formed from the primary tricyclic intermediates <jats:bold>A</jats:bold> <jats:italic>via</jats:italic> rearrangement (→heptalenedicarboxylates), <jats:italic>retro</jats:italic>‐<jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> reaction (→ azulenedicarboxylates), and <jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> reaction with ADM. The different reaction channels of <jats:bold>A</jats:bold> are dependent on the substituents. However, the main reaction channel of <jats:bold>A</jats:bold> is its <jats:italic>retro</jats:italic>‐<jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> reaction to the starting materials (azulene and ADM). The highly reversible <jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> reaction of ADM to the five‐membered ring of the azulenes is HOMO(azulene)/LUMO(ADM)‐controlled, in contrast to the at 200° irreversible ADM addition to the seven‐membered ring of the azulenes to yield the <jats:italic>Diels</jats:italic>‐<jats:italic>Alder</jats:italic> products of type <jats:bold>E</jats:bold>. This competing reaction must occur on grounds of orbital‐symmetry conservation under SHOMO(azulene)/LUMO(ADM) control (<jats:italic>cf. Schemes 20–22</jats:italic>). Several X‐ray diffraction analyses of the products were performed (<jats:italic>cf. Chapt. 4.1</jats:italic>).</jats:p>