1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

Abstract

Keywords: Allenes / Amines / Boranes / Cycloadditions / Eliminations / Strained molecules 3-Bromo-1-methyl-1,2,5,6-tetrahydropyridine(N−B)borane (7) was prepared from 3-bromopyridine by conversion to 3-bromo-1-methylpyridinium iodide, hydrogenation of the latter with sodium tetrahydroborate and treatment of the resulting 3-bromo-1-methyl-1,2,5,6-tetrahydropyridine (6) with borane−dimethyl sulfide. Whereas no trapping product of the possible intermediate 1-methyl-1-azacyclohexa-2,3-diene (4) could be observed on treatment of 6 with potassium tert-but-

Comprehensive Model for the Electronic Structures of 1,2,4-Cyclohexatriene and Related Compounds

“…This shows that the chemical nature of 3 + is very similar to that of 2 but distinctly different to that of 3 . This difference explains experimental findings from Christl et al, who found that a 1-aza-2,3-cyclohexadiene behaves completely different whether it has a three- or four-coordinated nitrogen atom …”

Comprehensive Model for the Electronic Structures of 1,2,4-Cyclohexatriene and Related Compounds

“…This shows that the chemical nature of 3 + is very similar to that of 2 but distinctly different to that of 3 . This difference explains experimental findings from Christl et al, who found that a 1-aza-2,3-cyclohexadiene behaves completely different whether it has a three- or four-coordinated nitrogen atom …”

Formation of anti‐Bredt‐type azabicyclo[4.2.0]octene frameworks through photochemical intramolecular [2+2] cycloaddition between indole and a distal double bond of allene

“…The structure of 2a was unambiguously determined by X‐ray crystallographic analysis (Figure 1). This kind of 2‐azabicyclo[4.2.0]oct‐5‐ene framework was previously synthesized via interception of 1‐azacyclohexa‐2,3‐diene with styrene, but a quite rare structure [38]. When isolated 2a or 3a was irradiated under the reaction conditions of Entry 7, it was recovered almost unchanged respectively.…”

Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds

“…Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. 184 − 190 After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure 19 . 191 , 192 Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 .…”

“…Our laboratory was particularly interested in heterocyclic allenes and the possibility of accessing them using Kobayashi-type precursors. Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. − After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure . , Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 . Three cycloadducts arising from azacyclic allene precursor 105 are shown reflective of (4 + 2), (3 + 2), and (2 + 2) cycloadditions (entries 1–3).…”

Comprehensive Model for the Electronic Structures of 1,2,4-Cyclohexatriene and Related Compounds

“…This shows that the chemical nature of 3 + is very similar to that of 2 but distinctly different to that of 3 . This difference explains experimental findings from Christl et al, who found that a 1-aza-2,3-cyclohexadiene behaves completely different whether it has a three- or four-coordinated nitrogen atom …”

Formation of anti‐Bredt‐type azabicyclo[4.2.0]octene frameworks through photochemical intramolecular [2+2] cycloaddition between indole and a distal double bond of allene

“…The structure of 2a was unambiguously determined by X‐ray crystallographic analysis (Figure 1). This kind of 2‐azabicyclo[4.2.0]oct‐5‐ene framework was previously synthesized via interception of 1‐azacyclohexa‐2,3‐diene with styrene, but a quite rare structure [38]. When isolated 2a or 3a was irradiated under the reaction conditions of Entry 7, it was recovered almost unchanged respectively.…”

Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds

“…Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. 184 − 190 After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure 19 . 191 , 192 Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 .…”

“…Our laboratory was particularly interested in heterocyclic allenes and the possibility of accessing them using Kobayashi-type precursors. Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. − After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure . , Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 . Three cycloadducts arising from azacyclic allene precursor 105 are shown reflective of (4 + 2), (3 + 2), and (2 + 2) cycloadditions (entries 1–3).…”

Comprehensive Model for the Electronic Structures of 1,2,4-Cyclohexatriene and Related Compounds

“…This shows that the chemical nature of 3 + is very similar to that of 2 but distinctly different to that of 3 . This difference explains experimental findings from Christl et al, who found that a 1-aza-2,3-cyclohexadiene behaves completely different whether it has a three- or four-coordinated nitrogen atom …”

Formation of anti‐Bredt‐type azabicyclo[4.2.0]octene frameworks through photochemical intramolecular [2+2] cycloaddition between indole and a distal double bond of allene

“…The structure of 2a was unambiguously determined by X‐ray crystallographic analysis (Figure 1). This kind of 2‐azabicyclo[4.2.0]oct‐5‐ene framework was previously synthesized via interception of 1‐azacyclohexa‐2,3‐diene with styrene, but a quite rare structure [38]. When isolated 2a or 3a was irradiated under the reaction conditions of Entry 7, it was recovered almost unchanged respectively.…”

Leveraging Fleeting Strained Intermediates to Access Complex Scaffolds

“…Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. 184 − 190 After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure 19 . 191 , 192 Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 .…”

“…Our laboratory was particularly interested in heterocyclic allenes and the possibility of accessing them using Kobayashi-type precursors. Many heterocyclic allenes had been accessed previously, but never using a silyl triflate as the precursor. − After developing syntheses of the appropriate precursors to azacyclic and oxacyclic allenes (i.e., 105 and 106 , respectively), we demonstrated their use in cycloaddition reactions, with select results shown in Figure . , Operationally, reactions are performed by treating the appropriate silyl triflate precursor ( 105 , X = NCbz; or 106 , X = O) with a trapping agent 18 in the presence of CsF at 23 °C, ultimately leading to cycloadducts 108 . Three cycloadducts arising from azacyclic allene precursor 105 are shown reflective of (4 + 2), (3 + 2), and (2 + 2) cycloadditions (entries 1–3).…”