Synthesis and Photophysical Properties of 3-Substituted-1H-Indazoles: A Pd-Catalyzed Double C-N Bond Formation Strategy via 1,6-Conjugate Addition.

A Pd-catalyzed cascade process for the direct synthesis of 3-substituted-1H-indazole employing p-quinone methide (p-QM) and arylhydrazine through Pd-catalyzed double C-N bond formation via 1,6-conjugate addition is reported. This reaction strategy affords efficient and practical access to synthetically important diverse 3-substituted-1H-indazoles in good yields. The photophysical properties of the synthesized 3-substituted-1H-indazoles are investigated, and some of them showed very good fluorescence properties with quantum yields up to 85%. Also, the synthesized 3-substituted-1H-indazole exhibits an acid-sensitive fluorescence turn-off activity.

Synthesis of π-Extended Benzofulvenes: A Pd-Catalyzed Cascade Annulation Process Comprising C-C Bond Formation Followed by 1,6-Conjugate Addition.

A Pd-catalyzed cascade annulation process comprising C-C bond formation followed by 1,6-conjugate addition for π-extended benzofulvenes is reported. This process is compatible with a wide range of functionalities for both the p-quinone methides and internal alkynes, leading to diverse π-extended benzofulvenes. Additionally, this strategy is also applicable for aryne annulation with p-quinone methides.

Pd-Catalyzed Alkyne and Aryne Annulations: Synthesis and Photophysical Properties of π-Extended Coumarins.

A Pd-catalyzed alkyne and aryne annulation strategy via C-H activation has been implemented for the synthesis of π-extended coumarins. This synthetic strategy provides a wide range of π-extended coumarins in moderate to good yields with good functional group compatibility. Photophysical properties of the synthesized π-extended coumarins have been evaluated, and some of them show interesting fluorescent properties. Three of the synthesized coumarins have been unambiguously established by a single-crystal XRD study.

Copper-Catalyzed Direct Syntheses of Phenoxypyrimidines from Chloropyrimidines and Arylboronic Acids: A Cascade Avenue and Unconventional Substrate Pairs.

This letter describes the first synthetic methodology for phenoxypyrimidines that avoids the direct use of phenols or their salts. In contrast to the general trend of delivering Suzuki-Miyaura cross-coupling products in reactions between aryl or alky halides and arylboronic acids, the substrate pairs used herein (chloropyrimidines and arylboronic acids) led to C-O bond formation under the reaction conditions. In total, 25 phenoxypyrimidines were successfully synthesized using the described protocol, 6 of which had a structural resemblance to etravirine.

Radiological risk estimation from indoor radon, thoron, and their progeny concentrations using nuclear track detectors.

In this paper, we report the results of seasonal variations of indoor radon and thoron concentrations, equilibrium factors for gas progeny, and radiological risks to dwellers in the hilly area of Guwahati City, Assam, India. Twin-cup dosemeters with LR-115 (II) nuclear track detectors were used in this study. The findings show that values vary significantly, with winter having the highest values and summer having the lowest, with spring and autumn having moderate values. In winter, radon concentrations range from 61.6 ± 11.2 Bq m-3 (Mud) to 115.3 ± 34.3 Bq m-3 (AT), with geometric mean values of 69.2 ± 13.8 Bq m-3 and 109.4 ± 27.9 Bq m-3, and in summer, they range from 21.1 ± 5.9 Bq m-3 (Mud) to 28.4 ± 8.3 Bq m-3 (AT), with geometric mean values of 22.7 ± 6.3 Bq m-3 and 26.1 ± 7.1 Bq m-3, whereas thoron concentrations range from 13.1 ± 5.1 Bq m-3 (Mud) to 58.8 ± 12.6 Bq m-3 (AT), with geometric mean values of 27.6 ± 7.0 Bq m-3 and 52.9 ± 10.1 Bq m-3 in winter, respectively, and in summer, from 8.8 ± 2.3 Bq m-3 (Mud) to 13.0 ± 5.5 Bq m-3 (Mud), with a geometric mean value of 1.87 ± 1.29 Bq m-3. Radon and thoron progeny levels are reported to vary from 4.1 ± 0.3 mWL (Mud) to 15.1 ± 4.3 mWL (AT) and 2.6 ± 0.9 mWL (Mud) to 14.3 ± 4.2 mWL (AT) in winter and from 1.5 ± 0.7 mWL (AT) to 3.0 ± 2.5 mWL (Mud) and 0.9 ± 0.3 mWL (AT) to 2.7 ± 0.5 mWL (Mud) in summer, respectively. The equilibrium factors for radon and its progeny have been reported to range from 0.23 ± 0.1 (Mud) to 0.51 ± 0.3 (AT) in winter, whereas from 0.23 ± 0.1 (AT) to 0.48 ± 0.4 (Mud) in summer, respectively. The equilibrium factors for thoron and its progeny have been estimated in the range of 0.02 ± 0.01 (Mud) to 0.09 ± 0.06 (AT) in winter, whereas 0.02 ± 0.02 (AT) to 0.07 ± 0.05 (Mud) in summer, respectively. The inhalation dose rates differed from house to house, having values in the range of 1.2 ± 0.2 mSv year-1 (Mud) to 4.6 ± 1.3 mSv year-1 (AT) in winter, whereas 0.5 ± 0.3 mSv year-1 (AT) to 0.9 ± 0.5 mSv year-1 (Mud) in summer, respectively. The effective doses (EDs) due to the exposure of radon and thoron in the study area have been found to range from 2.5 ± 0.3 mSv (Mud) to 9.1 ± 2.7 mSv (AT) in winter and 0.9 ± 0.4 mSv (AT) to 1.8 ± 1.3 mSv (Mud) in summer, respectively. The levels of radon and thoron in similar types of construction were found to be significantly different from one house to another. The estimated radon and thoron concentrations in the houses of that region during winter are found to be substantially higher than the global averages as reported by UNSCEAR.

o-Quinone Methides and o-Quinone Sulfides via Arynes: Synthesis of Ortho-Disubstituted Arenes and Heterocycles.

In recent decades, o-quinone methides and o-quinone sulfides have been extensively highlighted as reactive intermediates for the synthesis of diversely functionalized ortho-disubstituted arenes and heterocycles. Additionally, ortho-disubstituted arenes offer a constructive path for the synthesis of fused carbocycles, heterocycles, natural products, and drug candidates. In the lieu of that, this Synopsis highlights a comprehensive overview on the potential applications of in situ generated o-quinone methides and o-quinone sulfides for one-pot synthesis of ortho-disubstituted arenes and heterocycles via arynes.

Access to diverse organosulfur compounds via arynes: a comprehensive review on Kobayashi's aryne precursor.

Arynes are highly reactive transient intermediates having enormous applications in organic synthesis. In the last three decades aryne chemistry has shown incredible developments in carbon-carbon and carbon-heteroatom bond formation reactions. After the discovery of Kobayashi's protocol for the generation of aryne intermediates in a mild way, this field of chemistry witnessed rapid growth in synthetic organic chemistry. One aspect of development in this field involves C-S bond formation under mild conditions which has a tremendous scope for the synthesis of various important organosulfur building blocks.

Overview of coumarin-fused-coumarins: synthesis, photophysical properties and their applications.

Coumarin-fused-coumarins have attracted significant attention in the scientific world owing to their boundless applications in interdisciplinary areas. Various synthetic pathways have been developed to construct novel coumarin-fused-coumarin analogues by the fusion of modern methodologies with a classical Pechmann reaction or Knoevenagel condensation. Owing to their extended molecular framework, they possess interesting photophysical properties depending on the fused coumarin ring systems. This review highlights previously published reports on the synthetic strategies for structurally diverse coumarin-fused-coumarins. Furthermore, the scope of the synthesized biscoumarin-fused entities is described by highlighting their photophysical properties and applications.

A palladium-catalyzed cascade process for spirooxindole: an alternative way for the synthesis of spiro(indoline-3,2'-quinazolin)-2-ones.

A palladium-catalyzed cascade strategy has been developed for one-pot synthesis of functionalized spiro(indoline-3,2'-quinazolin)-2-one derivatives from readily available starting materials. The reaction proceeds via C-C and two C-N bond formations in a single reaction operation. This method offers an attractive pathway for the synthesis of a broad range of spiro(indoline-3,2'-quinazolin)-2-ones in good yields.

Pd(II)-Catalyzed oxidative alkenylation of 4-hydroxycoumarin with maleimide via a C-H bond activation strategy.

A Pd(ii)-catalyzed oxidative alkenylation of 4-hydroxycoumarins with maleimides for the synthesis of 4-hydroxy-3-maleimidecoumarins has been described. This methodology proceeds via C-H activation and C(sp2)-C(sp2) bond formation providing a series of alkenylated Heck-type products.

Exploration of Kobayashi's aryne precursor: a potent reactive platform for the synthesis of polycyclic aromatic hydrocarbons.

Arynes due to their transient nature leads to remarkable and versatile applications in the synthetic world. Apparently, researchers have focused on the construction of simple to complex π-conjugated systems using arynes as the reactive platform. In this regard, Kobayashi's aryne precursor has shown a great extent of reactivity and afforded significant advancement in the synthesis of polycyclic aromatic systems with wide practical utility. This review emphasizes the extensive utilization of Kobayashi's aryne intermediates and their derivatives for the synthesis of different classes of polycyclic aromatic hydrocarbons (PAHs).

Indane-Fused Spiropentadiene Chromanones: A Pd-Catalyzed Spiroannulation Followed by Cyclization via C-H Activation Strategy.

Pd-catalyzed spiroannulation of 4-bromocoumarin with alkynes has been illustrated. The reaction highlights an interesting process for cascade formation of two five-membered rings through spiroannulation followed by cyclization via C-H activation. This method offers an attractive platform for the synthesis of a broad range of indane-fused spiropentadiene chromanones in good yields.

Direct synthesis of ortho-methylthio allyl and vinyl ethers via three component reaction of aryne, activated alkene and DMSO.

A synthetic strategy has been developed for the direct synthesis of ortho-methylthio allyl and vinyl ethers via three-component reaction of in situ generated aryne, activated alkene and DMSO. This reaction proceeds via several bond cleavage and bond formation processes in a single operation. Mechanistic studies reveal that DMSO served as both a methylthiolating agent and an oxygen source. This synthetic method provides a wide range of ortho-methylthio-substituted arenes in good yields.

Recent advances in the synthesis of organophosphorus compounds via Kobayashi's aryne precursor: a review.

Organophosphorus compounds are important structural motifs that unveil enormous applications, particularly in the field of organic synthesis, agriculture, materials science and medicinal chemistry. Additionally, ortho-substituted arylphosphorus compounds have played an important role in homogeneous catalysis. Though there are several synthetic pathways for the synthesis of organophosphorus compounds, this review is particularly focused on aryne-based methodologies reported in the literature to date.

Three-Component Coupling Reactions of Aryne, DMSO, and Activated Alkyne: Stereoselective Synthesis of 2-[( o-Methylthio)aryloxy]-Substituted Dialkyl Maleates.

A transition-metal-free coupling reaction of aryne, DMSO, and activated alkyne for the synthesis of 2-[( o-methylthio)aryloxy]-substituted dialkyl maleates is reported. This cascade process is associated with several bond cleavage as well as bond formation reactions in one pot. One of our synthesized maleates has been unambiguously established by single-crystal XRD studies. This methodology allows preparation of trisubstituted vinyl ethers with excellent stereospecificity.

Transition-metal free C(sp2)-C(sp2) bond formation: arylation of 4-aminocoumarins using arynes as an aryl source.

A mild, efficient and transition-metal free synthetic strategy has been developed for the α-arylation of 4-aminocoumarins. This synthetic strategy proceeds via C(sp2)-C(sp2) bond formation between 4-aminocoumarins and aryne precursors in a single step by simple treatment with a fluoride source in the absence of a metal-catalyst. Moreover, this methodology affords good yields of 4-amino-3-arylcoumarin derivatives bearing halide functionality.

A cascade process for the synthesis of ortho-formyl allyl aryl ethers and 2H-chromen-2-ol derivatives from arynes via trapping of o-quinone methide with an activated alkene.

A transition-metal free synthetic strategy has been developed for the direct synthesis of ortho-formyl substituted allyl aryl ethers via a cascade three-component coupling of arynes, activated alkene and N,N-dimethylformamide. The reaction proceeds via C-O and C-C bond cleavage as well as C-C and two new C-O bond formations in a single reaction vessel. The methodology provides a good yield of ortho-formyl substituted allyl aryl ethers. Moreover, the synthetic strategy has been utilized for the one-pot synthesis of 2H-chromen-2-ol derivatives.

Aryne insertion into the P[double bond, length as m-dash]O bond: one-pot synthesis of quaternary phosphonium triflates.

A novel transition-metal free synthetic strategy has been developed for the direct synthesis of quaternary phosphonium triflates via insertion of aryne into phosphine oxide. This methodology provides good yields of quaternary phosphonium salts and one of the synthesized phosphonium salts has been unambiguously established by single crystal XRD study. Preliminary mechanistic studies suggest that the reaction proceeds via a sequential [2 + 2] cycloaddition followed by the o-arylation and protonation pathway.

Correction: A metal-free cascade reaction of ß-halo-α,ß-unsaturated aldehydes and 1,4-dithiane-2,5-diols: synthesis of polycyclic 2-formylthiophenes.

Correction for 'A metal-free cascade reaction of ß-halo-α,ß-unsaturated aldehydes and 1,4-dithiane-2,5-diols: synthesis of polycyclic 2-formylthiophenes' by Limi Goswami et al., Org. Biomol. Chem., 2017, 15, 6470-6473.

2,3-Diaroyl benzofurans from arynes: sequential synthesis of 2-aroyl benzofurans followed by benzoylation.

A cascade synthetic strategy for the direct synthesis of 2-aroyl benzofurans from aryne precursors has been developed. This reaction proceeds via C-O and C-C bond cleavage as well as C-O and C-C bond formation in a single reaction vessel. The methodology provides good yields of 2-aroyl benzofurans and tolerates a variety of functional groups. The synthesized 2-aroyl benzofurans were further benzoylated at 3-positions and one of the synthesized 2,3-diaroyl benzofuran structures was confirmed unambiguously by X-ray crystallography.