Model Reactions for the Synthesis of Azacorannulenes and Related Heteroaromatic Compounds

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis, Eu3+ Multiphoton Sensitization and Imaging Applications

“…Reported approaches to benzo[ h ]isoquinoline scaffold are not suitable to obtain 1,3-asymmetric compound B[h]IQ unless major modifications leading to significant increase in synthetic process complexity are implemented [ 34 , 35 , 36 , 37 ]. From a synthetic perspective, the major hurdle is represented by the lack of reactivity of the position 3 [ 38 ] Some examples of unsubstituted scaffolds were synthesized starting from 3-ethynyl−2-phenylpyridine through a pyrolysis process [ 34 ], or alternatively by a Pomeranz–Fritsch procedure from naphthaldehydes [ 35 ], 3,4-disubstituted (mainly with aryl fragments) benzo[ h ]isoquinolines were obtained from (1-naphthylmethyl)amine through a rhodium-catalyzed coupling reaction [ 37 ], and a 1,3-dimethyl derivative has been prepared through a Suzuki or Negishi cross-coupling followed by a cyclization reaction induced by t-BuOK [ 36 ]. In this context, we planned our synthesis by building the heteroaromatic fragment already substituted in the desired positions ( Scheme 2 ).…”

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis, Eu3+ Multiphoton Sensitization and Imaging Applications

“…Reported approaches to benzo[ h ]isoquinoline scaffold are not suitable to obtain 1,3-asymmetric compound B[h]IQ unless major modifications leading to significant increase in synthetic process complexity are implemented [ 34 , 35 , 36 , 37 ]. From a synthetic perspective, the major hurdle is represented by the lack of reactivity of the position 3 [ 38 ] Some examples of unsubstituted scaffolds were synthesized starting from 3-ethynyl−2-phenylpyridine through a pyrolysis process [ 34 ], or alternatively by a Pomeranz–Fritsch procedure from naphthaldehydes [ 35 ], 3,4-disubstituted (mainly with aryl fragments) benzo[ h ]isoquinolines were obtained from (1-naphthylmethyl)amine through a rhodium-catalyzed coupling reaction [ 37 ], and a 1,3-dimethyl derivative has been prepared through a Suzuki or Negishi cross-coupling followed by a cyclization reaction induced by t-BuOK [ 36 ]. In this context, we planned our synthesis by building the heteroaromatic fragment already substituted in the desired positions ( Scheme 2 ).…”

Blue Fluorescent 4a-Aza-4b-boraphenanthrenes

“…The reaction of 1-chloro-2-trimethylsilyl-boracyclohexa-2,5-diene with a variety of 2-ethynyl-pyridines was found to cleanly afford the desired phenanthrene analogues 1 − 3 5 (Scheme ) with BN-substitution at the internal 4a,4b positions. The cycloisomerization of the pendent ethynyl group was found to be unusually facile, as similar transformations in all-carbon 6 or other heteroaromatic systems 7 are typically incurred via a soft metal catalyst, UV irradiation, or flash vacuum pyrolysis . The observed increase in reactivity in this case may be due to the enhanced nucleophilic nature of the carbon atom α to boron in the borabenzene−pyridine adduct intermediates 1 ‘− 5 ‘.…”

Azaindenocorannulenes: Synthesis, Properties, and Chirality

“…Recent advances in the synthesis of indenocorannulenes enable the synthesis of pyridinoid bowls, with nitrogen replacing rim-CH groups of indenocorannulene . Introduction of heteroatoms into curved aromatic structures enables one to tailor the optoelectronic properties of the carbon bowl-shaped motifs. − In particular, doping of nitrogen into the indole core analog of corannulene , and the aza-sumanene series has shown to enable unique tuning of their electrochemical, photophysical, and bowl-dynamic properties (Figure ). Resolution-epimerization studies of a chiral monoaza-diindeno­corannulene­imide 9 reveals that even simple chiral bowl derivatives can exceed the configurational stability of phosphines, o,o′,o″,o′″-substituted biaryls, and extended helicenes, making higher order indenocorannulenes attractive targets for future studies of kinetically inert chiral scaffolds.…”

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis, Eu3+ Multiphoton Sensitization and Imaging Applications

“…Reported approaches to benzo[ h ]isoquinoline scaffold are not suitable to obtain 1,3-asymmetric compound B[h]IQ unless major modifications leading to significant increase in synthetic process complexity are implemented [ 34 , 35 , 36 , 37 ]. From a synthetic perspective, the major hurdle is represented by the lack of reactivity of the position 3 [ 38 ] Some examples of unsubstituted scaffolds were synthesized starting from 3-ethynyl−2-phenylpyridine through a pyrolysis process [ 34 ], or alternatively by a Pomeranz–Fritsch procedure from naphthaldehydes [ 35 ], 3,4-disubstituted (mainly with aryl fragments) benzo[ h ]isoquinolines were obtained from (1-naphthylmethyl)amine through a rhodium-catalyzed coupling reaction [ 37 ], and a 1,3-dimethyl derivative has been prepared through a Suzuki or Negishi cross-coupling followed by a cyclization reaction induced by t-BuOK [ 36 ]. In this context, we planned our synthesis by building the heteroaromatic fragment already substituted in the desired positions ( Scheme 2 ).…”

Blue Fluorescent 4a-Aza-4b-boraphenanthrenes

“…The reaction of 1-chloro-2-trimethylsilyl-boracyclohexa-2,5-diene with a variety of 2-ethynyl-pyridines was found to cleanly afford the desired phenanthrene analogues 1 − 3 5 (Scheme ) with BN-substitution at the internal 4a,4b positions. The cycloisomerization of the pendent ethynyl group was found to be unusually facile, as similar transformations in all-carbon 6 or other heteroaromatic systems 7 are typically incurred via a soft metal catalyst, UV irradiation, or flash vacuum pyrolysis . The observed increase in reactivity in this case may be due to the enhanced nucleophilic nature of the carbon atom α to boron in the borabenzene−pyridine adduct intermediates 1 ‘− 5 ‘.…”

Azaindenocorannulenes: Synthesis, Properties, and Chirality

“…Recent advances in the synthesis of indenocorannulenes enable the synthesis of pyridinoid bowls, with nitrogen replacing rim-CH groups of indenocorannulene . Introduction of heteroatoms into curved aromatic structures enables one to tailor the optoelectronic properties of the carbon bowl-shaped motifs. − In particular, doping of nitrogen into the indole core analog of corannulene , and the aza-sumanene series has shown to enable unique tuning of their electrochemical, photophysical, and bowl-dynamic properties (Figure ). Resolution-epimerization studies of a chiral monoaza-diindeno­corannulene­imide 9 reveals that even simple chiral bowl derivatives can exceed the configurational stability of phosphines, o,o′,o″,o′″-substituted biaryls, and extended helicenes, making higher order indenocorannulenes attractive targets for future studies of kinetically inert chiral scaffolds.…”

New 1,3-Disubstituted Benzo[h]Isoquinoline Cyclen-Based Ligand Platform: Synthesis, Eu3+ Multiphoton Sensitization and Imaging Applications

“…Reported approaches to benzo[ h ]isoquinoline scaffold are not suitable to obtain 1,3-asymmetric compound B[h]IQ unless major modifications leading to significant increase in synthetic process complexity are implemented [ 34 , 35 , 36 , 37 ]. From a synthetic perspective, the major hurdle is represented by the lack of reactivity of the position 3 [ 38 ] Some examples of unsubstituted scaffolds were synthesized starting from 3-ethynyl−2-phenylpyridine through a pyrolysis process [ 34 ], or alternatively by a Pomeranz–Fritsch procedure from naphthaldehydes [ 35 ], 3,4-disubstituted (mainly with aryl fragments) benzo[ h ]isoquinolines were obtained from (1-naphthylmethyl)amine through a rhodium-catalyzed coupling reaction [ 37 ], and a 1,3-dimethyl derivative has been prepared through a Suzuki or Negishi cross-coupling followed by a cyclization reaction induced by t-BuOK [ 36 ]. In this context, we planned our synthesis by building the heteroaromatic fragment already substituted in the desired positions ( Scheme 2 ).…”

Blue Fluorescent 4a-Aza-4b-boraphenanthrenes

“…The reaction of 1-chloro-2-trimethylsilyl-boracyclohexa-2,5-diene with a variety of 2-ethynyl-pyridines was found to cleanly afford the desired phenanthrene analogues 1 − 3 5 (Scheme ) with BN-substitution at the internal 4a,4b positions. The cycloisomerization of the pendent ethynyl group was found to be unusually facile, as similar transformations in all-carbon 6 or other heteroaromatic systems 7 are typically incurred via a soft metal catalyst, UV irradiation, or flash vacuum pyrolysis . The observed increase in reactivity in this case may be due to the enhanced nucleophilic nature of the carbon atom α to boron in the borabenzene−pyridine adduct intermediates 1 ‘− 5 ‘.…”

Azaindenocorannulenes: Synthesis, Properties, and Chirality

“…Recent advances in the synthesis of indenocorannulenes enable the synthesis of pyridinoid bowls, with nitrogen replacing rim-CH groups of indenocorannulene . Introduction of heteroatoms into curved aromatic structures enables one to tailor the optoelectronic properties of the carbon bowl-shaped motifs. − In particular, doping of nitrogen into the indole core analog of corannulene , and the aza-sumanene series has shown to enable unique tuning of their electrochemical, photophysical, and bowl-dynamic properties (Figure ). Resolution-epimerization studies of a chiral monoaza-diindeno­corannulene­imide 9 reveals that even simple chiral bowl derivatives can exceed the configurational stability of phosphines, o,o′,o″,o′″-substituted biaryls, and extended helicenes, making higher order indenocorannulenes attractive targets for future studies of kinetically inert chiral scaffolds.…”