Synthesis and biological evaluation of 1-amino isochromans from 2-bromoethyl benzaldehyde and amines in acid medium.

We have developed a facile and efficient synthetic route to substituted isochromans for the first time by reacting 2-(2-bromoethyl)benzaldehyde with a variety of aryl, heteroaryl amines in AcOH. The reaction is catalyst/additive free and takes place at reflux conditions with short reaction time to furnish products in good to excellent yields. All the compounds have been characterized by spectral techniques such as IR, 1H NMR and Mass etc. Synthesized compounds were evaluated for antimicrobial activity against specific bacterial like 1) Staphylococcus strains aureus 2) Bacillus subtilis 3) Escherichia coli 4) Pseudomonas aeruginosa. Compounds 3e, 3n, 3 m, 3 l, 3 k, 3j and 3b showed most potent in vitro activity against bacterial strains.

Sequential aza-Piancatelli rearrangement/Friedel-Crafts alkylation for the synthesis of pyrrolo[1,2-d]benzodiazepine derivatives.

2-Furylcarbinols undergo a smooth aza-Piancatelli rearrangement followed by Friedel-Crafts alkylation with a bifunctional substrate, (1H-pyrrol-1-yl)aniline, in the presence of 10 mol% In(OTf)3 in acetonitrile at room temperature to afford the corresponding hexahydrobenzo[b]cyclopenta[f]pyrrolo[1,2-d][1,4]diazepin-11(4aH)-one scaffolds in good yields. This method offers significant advantages such as high conversions, mild reaction conditions, short reaction times, and high selectivity. The relative stereochemistry of the product was established by nOe studies.

Domino Strategy for the Stereoselective Construction of Angularly Fused Tricyclic Ethers.

A stereoselective synthesis of decahydrofuro[3,2-d]isochromene derivatives has been achieved by the condensation of 2-cyclohexenylbutane-1,4-diol with aldehydes in the presence of a stochiometric amount of BF3·OEt2 in dichloromethane at -78 °C. Similarly, the condensation of 2-cyclopentenylbutan-1,4-diol with aldehydes provides the corresponding octahydro-2H-cyclopenta[c]furo[2,3-d]pyran derivatives in good yields with high diastereoselectivity. It is an elegant strategy for the quick construction of tricyclic architectures with four contiguous stereogenic centers in a single step. These tricyclic frameworks are the integral part of numerous natural products.

Synthesis and biological evaluation of phaitanthrin congeners as anti-mycobacterial agents.

Natural alkaloid, tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione) and its analogues are found to exhibit potent anti-tubercular activity against MDR-TB. A novel class of indolo[2,1-b]quinazolinones have been synthesized to evaluate their anti-mycobacterial activity. Enoyl-acyl carrier protein reductase (InhA) of Mycobacterium tuberculosis is one of the key enzymes and has been validated as an effective anti-microbial target. In silico molecular docking study demonstrates that the synthesized compounds exhibit high affinity for the M. tuberculosis drug target InhA. Phaitanthrin is a natural product, which belongs to a family of tryptanthrin and exhibits structural similarity except at position 6. Phaitanthrin derivatives are prepared by modifying the keto functionality of tryptanthrin. These phaitanthrin congeners are found to display promising anti-tubercular activity.

Stereoselective synthesis of octahydrocyclohepta[c]pyran-6(1H)-one scaffolds through a Prins/alkynylation/hydration sequence.

Aldehydes undergo a smooth coupling with (E/Z)-non-3-en-8-yn-1-ol in the presence of 10 mol% of CuX and BF3·OEt2 under mild conditions to produce a novel class of octahydrocyclohepta[c]pyran-6(1H)-one derivatives in good yields with excellent diastereoselectivity through a sequential Prins/alkynylation/hydration. This is the first report on the termination of Prins cyclization with a tethered alkyne.

Domino Prins/pinacol reaction for the stereoselective synthesis of spiro[pyran-4,4'-quinoline]-2',3'-dione derivatives.

A wide array of aldehydes undergo smooth cross-coupling with 3-hydroxy-3-(4-hydroxybut-1-en-2-yl)-1-methylindolin-2-one in the presence of 10 mol% BF3·OEt2 at 0 °C in dichloromethane to afford the corresponding 2,3,5,6-tetrahydro-1'H-spiro[pyran-4,4'-quinoline]-2',3'-dione derivatives in good yields with excellent diastereoselectivity. This is the first report on the synthesis of tetrahydro-1'H-spiro[pyran-4,4'-quinoline]-2',3'-dione scaffolds through a cascade of Prins/pinacol reactions.

An iodine catalyzed metal free domino process for the stereoselective synthesis of oxygen bridged bicyclic ethers.

A domino reaction has been developed for the synthesis of oxygen bridged bicyclic ethers through the coupling of 4-(2-hydroxyethyl)cyclohex-3-enols with aldehydes in the presence of 10 mol% of molecular iodine in dichloromethane at 25 °C. This method is highly diastereoselective affording the corresponding bicyclic ethers, i.e. octahydro-4a,7-epoxyisochromenes in good yields with high selectivity. It is the first report on the synthesis of oxygen bridged bicyclic ethers using a domino Prins strategy.

A novel Prins cascade process for the stereoselective synthesis of oxa-bicycles.

E- and Z-9-Methyldeca-3,8-dien-1-ols undergo smooth cyclization with aldehydes in the presence of 20 mol% AgSbF6 under extremely mild conditions to generate the corresponding oxa-bicycles in good yields with excellent selectivity. In fact, E-olefin affords the trans-product exclusively, whereas the Z-olefin gives the cis-product predominantly. In the case of E- or Z-8-methylnona-3,8-dien-1-ol, the product is formed via the termination of Prins cyclization with an allylic C-H bond through olefin migration. The termination of Prins cyclization with tethered olefin is an unprecedented reaction, which provides a useful motif of various natural products.

Prins cascade cyclization for the synthesis of 1,9-dioxa-4-azaspiro[5.5]undecane derivatives.

A novel Prins cascade process for the synthesis of 1,9-dioxa-4- azaspiro[5.5]undecane derivatives by the coupling of aldehydes with N-(4-hydroxy-2-methylenebutyl)-N-(2-hydroxyethyl)-4-methylbenzenesulfonamide has been developed. This is the first report of the synthesis of spiromorpholinotetrahydropyran derivatives through a Prins bicyclization.

Tuning the reactivity of oxygen/sulfur by acidity of the catalyst in Prins cyclization: oxa- versus thia-selectivity.

An unprecedented oxa- versus thia-selectivity has been observed in Prins cyclization of 6-mercaptohex-3-en-1-ol with aldehydes. In the presence of a stoichiometric amount of strong Lewis or Brønsted acids, the reaction provides the hexahydro-2H-thieno[3,2-c]pyran skeleton predominantly via oxonium-Prins cyclization. In contrast, a catalytic amount of weak Lewis or Brønsted acids provides the hexahydro-2H-thiopyrano[4,3-b]furan preferentially through thionium-Prins cyclization.

Thee-component, one-pot synthesis of hexahydroazepino[3,4-b]indole and tetrahydro-1H-pyrido[3,4-b]indole derivatives and evaluation of their cytotoxicity.

A three-component, four-center Ugi reaction has been developed to produce a novel class of 2-aryl-3-oxo-hexahydroazepino[3,4-b]indole and 2-aryl-3-oxo-tetrahydro-1H-pyrido[3,4-b]indole derivatives in good to high yields. A few of them exhibit moderate cytotoxicity against various cancer cell lines such as HeLa (human epithelial cervical cancer), A549 (human lung carcinoma epithelial), DU145 (human prostate carcinoma epithelial) and MCF-7 (human breast adenocarcinoma).

First example of quinine-squaramide catalyzed enantioselective addition of diphenyl phosphite to ketimines derived from isatins.

A highly enantioselective addition of diphenyl phosphite to ketimines derived from isatins has been achieved using a bifunctional organocatalyst, quinine-derived squaramide catalyst. This method works efficiently with several ketimines to produce the corresponding 3-amino-2-oxoindolin-3-yl-phosphonates in excellent yields with high enantioselectivity (up to 98% ee).

Acetal-initiated Prins bicyclization for the synthesis of hexahydrofuro-[3,4-c]furan lignans and octahydropyrano[3,4-c]pyran derivatives.

An acetal-initiated Prins bicyclization approach has been developed for the stereoselective synthesis of hexahydrofuro[3,4-c]furan lignans. This also provides a direct way to generate a new series of octahydropyrano[3,4-c]pyran derivatives in a single-step process.

Tandem Prins/pinacol reaction for the synthesis of oxaspiro[4.5]decan-1-one scaffolds.

A novel Lewis acid catalyzed Prins/pinacol cascade process has been developed for the synthesis of 7-substituted-8-oxaspiro[4.5]decan-1-ones in good yields with excellent selectivity. This is the first example of the synthesis of oxaspirocycles from aldehydes and 1-(4-hydroxybut-1-en-2-yl)cyclobutanol through a cascade of Prins/pinacol rearrangement. This method is applicable to a wide range of aldehydes such as aromatic, aliphatic, heteroaromatic, and α,ß-unsaturated aldehydes.

Visible Light-Induced Metal-free Arylation of Coumarin-3-carboxylates with Arylboronic Acids.

The present work represents a novel methodology for the selective arylation of coumarin-3-carboxylates with arylboronic acids via a photochemical route, marking the first-ever attempt for the direct alkenyl C-H arylation using rose bengal as a photocatalyst, which is a readily available and cost-effective alternative to transition metal catalysis. The reaction proceeds smoothly in MeOH/H2O solvent media in the presence of radical initiator affording the arylated products in good yields (60-80 %). The reaction parameters such as visible light, radical initiator, oxidant, anhydrous solvent, and inert atmosphere play a crucial role for the success of this methodology. The substituents present on the substrate show a significant effect on the conversion. This study provides a valuable contribution to the field of organic synthesis offering a new and efficient approach to the arylation of coumarin-3-carboxylic acid esters with a broad substrate scope and high functional group tolerance. It is a versatile method and provides a direct access to biologically relevant 4-arylcoumarin-3-carboxylates.

Stereoselective synthesis of hexahydro-1H-pyrano- and thiopyrano[3,4-c]quinoline derivatives through a Prins cascade cyclization.

A cascade reaction of (E)-5-(arylamino)pent-3-en-1-ols and thiols with various aldehydes in the presence of 30 mol % BF3·OEt2 in 1,2-dichloroethane at 80 °C affords a novel class of trans-fused hexahydro-1H-pyrano[3,4-c]quinolines and hexahydro-1H-thiopyrano[3,4-c]quinolines in good to excellent yields with high selectivity. The condensation of (Z)-5-(arylamino)pent-3-en-1-ol with aldehydes provides the corresponding cis-fused products under similar conditions.

Thia-prins bicyclization approach for the stereoselective synthesis of dithia- and azathia-bicycles.

A novel thia-Prins bicyclization approach has been developed for the first time for the synthesis of hexahydro-2H-thieno[3,2-c]thiopyran derivatives from the coupling of homoallylic mercaptans such as hex-3-ene-1,6-dithiol with various aldehydes using 10 mol % InBr3 in dichloromethane with high selectivity. In addition, the coupling of (E)-N-(6-mercaptohex-3-enyl)-4-methylbenzenesulfonamide with aldedydes affords the corresponding N-tosyloctahydrothiopyrano[4,3-b]pyrrole derivatives in good yields. This reaction is a stereoselective affording trans-fused product from E-homoallyllic mercaptan and cis-fused product from Z-homoallyllic mercaptan.

Aminoclay-supported copper nanoparticles for 1,3-dipolar cycloaddition of azides with alkynes via click chemistry.

Aminoclay supported copper nanoparticles are effective in promoting [3+2] cycloaddition of azides with terminal alkynes to produce the corresponding 1,2,3-triazoles in excellent yields. The copper nanoparticles are highly reactive in water and can be recycled for four cycles with consistent activity.

A domino Knoevenagel hetero-Diels-Alder reaction for the synthesis of polycyclic chromene derivatives and evaluation of their cytotoxicity.

A novel octahydrochromeno[4,3-a]xanthen-1(2H)-one derivatives has been prepared using 10mol% dl-proline in ethanol via a domino Knoevenagel hetero-Diels-Alder reaction of alkene-tethered chromene-3-carboxaldehyde with cyclic 1,3-diketones. This is not only the first example on the preparation of highly diastereoselective pentacyclic chromene derivatives from alkene appended chromene-3-carboxaldehyde in one-pot process at ambient temperature but also preliminary evaluation of the cytotoxic activity of these chromene derivatives. Some of these compounds are found to exhibit potent cytotoxicity against two carcinoma cell lines A549 and B-16.

Enantioselective Friedel-Crafts alkylation of indoles with 2-enoylpyridine-N-oxides catalyzed by glucoBOX-Cu(II) complex.

The glucosamine derived glucoBOX-Cu(II) complex was found to be a unique catalytic system for enantioselective Friedel-Crafts alkylation of indoles with 2-enoylpyridine-1-oxides. A large number of 3-alkylated indole derivatives were prepared using 5 mol% glucoBOX-Cu(II) complex in excellent yields with high enantioselectivity up to 99% ee.