Kiran Indukuri

Stereoselective Synthesis of Amido and Phenyl Azabicyclic Derivatives via a Tandem Aza Prins-Ritter/Friedel–Crafts Type Reaction of Endocyclic N-Acyliminium Ions

A simple protocol is described for the synthesis of amido and phenyl hexahydroindolizin-3(2H)-one, hexahydro-1H-quinolizin-4(6H)-one, and 1,3,4,10b-tetrahydropyrido[2,1-a]isoindol-6(2H)-one derivatives via endo-trig (aza-Prins type) cyclization followed by an intermolecular Ritter/Friedel-Crafts reaction of cyclic N-acyliminium ions, which are derived from the boron trifluoride etherate treatment of regioselectively reduced N-homoallyl imides. The reactions are highly diastereoselective with excellent yields.

Unveiling the mode of action of antibacterial labdane diterpenes from Alpinia nigra (Gaertn.) B. L. Burtt seeds.

The labdane diterpene, (E)-labda-8(17), 12-diene-15, 16-dial (compound A) and its epoxide analogue, (E)-8β, 17-Epoxylabd-12-ene-15, 16-dial (compound B) were isolated from the seeds of Alpinia nigra for the first time. The antibacterial activities of both compounds were evaluated against three Gram-positive and four Gram-negative bacteria, and flow cytometric analysis revealed that these compounds caused significant damage to the bacterial cell membranes. Further, field emission scanning electron microscope imaging and cell leakage analysis confirmed that the labdane diterpenes were responsible for bacterial cell membrane damage and disintegration. Our findings provide new insight into the broad-spectrum effects of two natural labdane diterpenes that may be useful in the future development of herbal antibiotic products.

Diastereoselective Synthesis of Substituted Tetrahydrothiopyrans via (3,5)-Thionium–Ene Cyclization Reaction

Tetrahydrothiopyrans have been efficiently synthesized in good yields with excellent diastereoselectivity from aldehydes and substituted 5-methylhex-4-ene-1-thiol via (3,5)-thionium-ene cyclization reaction mediated by boron trifluoride etherate.

Diastereoselective Synthesis of Dihydropyrans via Prins Cyclization of Enol Ethers: Total Asymmetric Synthesis of (+)-Civet Cat Compound

Trimethylsilyl trifluoromethanesulfonate (TMSOTf) can be efficiently used for Prins cyclization of acrylyl enol ethers to 5,6-dihydro-2H-pyran-2-acetates stereo- and regioselectively in good yields. The methodology was used for the total synthesis of natural product (+)-civet.

Synthesis of Five-, Six-, and Seven-Membered 1,3- and 1,4-Heterocyclic Compounds via Intramolecular Hydroalkoxylation/Hydrothioalkoxylation of Alkenols/Thioalkenols.

Intramolecular hydroalkoxylation/hydrothioalkoxylation of nitrogen-tethered alkenes and alcohols/thiols mediated by boron trifluoride etherate leads to five-membered thiazolidine, six-membered 1,4-oxazines (morpholines) and tetrahydro-2H-1,4-thiazines (thiomorpholines), and seven-membered 1,4-oxazepanes in good yields.

Lewis Acid Mediated Intramolecular C–C Bond Formation of Alkyne-Epoxide Leading to Six-Membered Nitrogen and Oxygen Heterocycles

Intramolecular C-C bond formation of oxygen- and nitrogen-tethered alkynes and epoxide mediated by Lewis acid under ambient conditions is described. A simple procedure for the synthesis of 3,6- and 5,6-dihydropyrans and 3,4-dehydropiperidines from acyclic building blocks in good yields without using any transition metal is shown.

Diastereoselective synthesis of substituted tetrahydrothiophenes and -thiopyrans via thia-Prins cyclization reaction.

Tetrahydrothiophenes and -thiopyrans have been efficiently synthesized from thioacrylates via thia-Prins cyclization reaction mediated by trimethylsilyltrifluoromethanesulfonate with good diastereoselectivity and in good to high yields.

Regioselective one-pot, three-component synthesis of substituted 2H-indazoles from 2-nitroarylaldehyde, alkyne and amine catalyzed by the CuBr/Zn(OTf)2 system

3-(Arylethynyl)-2H-indazoles can be effectively synthesized in one-pot using 2-nitroarylaldehydes, primary amines and alkynes co-catalyzed by copper(I) bromide and zinc(II) triflate. This method has a broad substrate scope with high to medium tolerance for a variety of functional groups.

Synthesis of 2,3-dihydro-4-pyranones from epoxides via intermolecular [4+2] cycloaddition reaction

An efficient synthesis of 2,3-dihydro-4-pyranones from epoxides and 3-alkoxycyclobutanones via an intermolecular [4+2] cycloaddition reaction, mediated by boron trifluoride etherate has been developed. The reaction is diastereoselective and gives trans diastereomers in excess.