Applications of [4+2] Anionic Annulation and Carbonyl-Ene Reaction in the Synthesis of Anthraquinones, Tetrahydroanthraquinones, and Pyranonaphthoquinones

Hexa-2,5-dienoates, susceptible to isomerization by acids and bases, are suitable for the [4+2] anionic annulation to give 3-(2-alkenyl)­naphthoates in regiospecific manner. When combined with intramolecular carbonyl-ene reaction (ICE), the accessibility of the naphthoates culminates in a new synthesis of anthraquinones and diastereoselective synthesis of tetrahydroanthraquinones. This strategy has also resulted in a 3-step synthesis of dehydroherbarin from a 3-methallylnaphthoate

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

Experiment and Computational Study on the Regioselectivity of Nucleophilic Addition to Unsymmetrical <i>p</i>‑Benzynes Derived from Bergman Cyclization of Enediynes

The regioselectivity in addition of nucleophiles to the <i>p</i>-benzyne intermediates derived from unsymmetrical aza-substituted enediynes via Bergman cyclization was studied. Computational studies [using UB3LYP/6-31G­(d,p) level of theory] suggest that the <i>p</i>-benzyne intermediate retains its similar electrophilic character at the two radical centers even under unsymmetrical electronic perturbation, thus supporting the predicted model of nucleophilic addition to <i>p</i>-benzyne proposed by Perrin and co-workers (Perrin et al. <i>J. Am. Chem. Soc.</i> <b>2007</b>, <i>129</i>, 4795–4799) and later by Alabugin and co-workers (Peterson et al. <i>Eur. J. Org. Chem.</i> <b>2013</b>, <i>2013</i>, 2505–2527). However, observed experimental results suggest that there was small but definite regioselectivity (∼5–25%), the extent varying with the electronic nature of the substituents. Differential solvated halide ion concentrations around the vicinity of two radical centers arising due to surrounding surface electrostatic potential (computationally calculated) may be one of the possible factors for such selectivity in some of the examined <i>p-</i>benzynes. However, other complicated dynamical issues like the trajectory of the attacking nucleophile to the radical center which can be influenced by electronic and/or steric perturbation of starting enediyne conformation cannot be ruled out. The overall yield of the anionic addition was in the range of 80–99%

B(C6F5)3-Catalyzed Direct C3 Alkylation of Indoles and Oxindoles

The direct C3 alkylation of indoles and oxindoles is a challenging transformation, and only a few direct methods exist. Utilizing the underexplored ability of triaryl boranes to mediate the heterolytic cleavage of α-nitrogen C–H bonds in amines, we have developed a catalytic approach for the direct C3 alkylation of a wide range of indoles and oxindoles using amine-based alkylating agents. We also employed this borane-catalyzed strategy in an alkylation-ring opening cascade

Electron deficient borane-mediated hydride abstraction in amines: stoichiometric and catalytic processes

The manipulation of amino C-H bonds has garnered significant interest from the synthetic community due to its inherently high atom, step and redox economy. This Tutorial Review summarises the ability of boranes to mediate hydride abstraction from α-amino and γ-amino conjugated C-H bonds. Borane-mediated hydride abstraction results in the generation of reactive iminium hydridoborate salts that participate in a variety of stoichiometric and catalytic processes. The reactions that have utilised this unusual reactivity include those that manipulate amino scaffolds (including dehydrogenation, racemisation, isomerisation, α- and β-functionalisation, and C-N bond cleavage) and those that use amine-based reagents (transfer hydrogenation, and alkylation)