P[N(i-Bu)CH(2)CH(2)](3)N: nonionic Lewis base for promoting the room-temperature synthesis of α,β-unsaturated esters, fluorides, ketones, and nitriles using Wadsworth-Emmons phosphonates

The bicyclic triaminophosphine P(RNCH(2)CH(2))(3)N (R = i-Bu, 1c) serves as an effective promoter for the room-temperature stereoselective synthesis of α,β-unsaturated esters, fluorides, and nitriles from a wide array of aromatic, aliphatic, heterocyclic, and cyclic aldehydes and ketones, using a range of Wadsworth-Emmons (WE) phosphonates. Among the analogues of 1c [R = Me (1a), i-Pr (1b), Bn (1d)], 1a and 1b performed well, although longer reaction times were involved, and 1d led to poorer yields than 1c. Functionalities such as cyano, chloro, bromo, methoxy, amino, ester, and nitro were well tolerated. We were able to isolate and characterize (by X-ray means; see above) the reactive WE intermediate species formed from 2b and 1c.     

Sc(OTf)3-catalyzed one-pot ene-Prins cyclization: a novel synthesis of octahydro-2H-chromen-4-ols

(R)-Citronellal undergoes initial ene reaction followed by Prins cyclization with aldehydes in the presence of 5 mol % of scandium triflate at ambient temperature to furnish octahydro-2H-chromen-4-ols in good yields and with high cis-selectivity. The use of scandium triflate makes this procedure simple, more convenient, and practical.     

Synthesis and antimicrobial study of linked heterocyclics containing Pyrazole-pyrimidine-thiazolidin-4-one

A new series of linked heterocyclics, 3-[4-(4-chlorophenyl)-6-(3,5-dimethyl-1-phenyl-1H-4-pyrazolyl)-2-pyrimidinyl]-2-(aryl/heteryl)-1,3-thiazolan-4-ones (6a-j), has been synthesized by the one-pot cyclo-condensation of 4-(4-chlorophenyl)-6-(3,5-dimethyl-1-phenyl-1H-4-pyrazolyl)-2-pyrimidinamine (5), aryl/heteroaryl aldehyde and thioglycolic acid. The structures of the synthesized compounds have been confirmed via IR, (1)H-NMR, (13)C-NMR, MS and elemental analyses. Further, all the newly synthesized compounds 6a-j have been assayed for their antimicrobial activity against Gram-positive and Gram-negative bacteria and fungi. The compounds containing moieties like 4-nitrophenyl (6c), 3-nitrophenyl (6d), 4-dimethylaminophenyl (6g), 2-furyl (6i) and 1,3-benzodioxole (6j), at 2-position of thiazolidin-4-one ring exhibited good inhibitory activity against all the tested organisms.     

Stereoselective formal synthesis of aspergillide A

The stereoselective formal synthesis of aspergillide A (1), a cytotoxic 14-membered macrolide, is disclosed. The key intermediate, a trisubstituted tetrahydropyran core is prepared by SmI₂-induced intramolecular reductive cyclization as well as by using sequential α-aminooxylation, Horner-Wadsworth-Emmons olefination, and followed by Oxa-Michael cyclization. Other notable transformations in the synthesis include the use of Jacobsen’s hydrolytic kinetic resolution, esterification, ring-closing metathesis (RCM), and cross-metathesis (CM) reactions.     

Total synthesis of cryptopyranmoscatone B1 from 3,4,6-tri-O-acetyl-d-glucal

The first stereoselective total synthesis of the natural cryptopyranmoscatone B1 has been accomplished from 3,4,6-tri-O-acetyl-d-glucal. In addition to the double cross-metathesis reaction, a tandem nucleophilic addition-diastereoselective reduction of an in situ generated oxocarbenium cation have been used as key steps to assemble the glycoside moiety of the target molecule.     

The silylalkyne-Prins cyclization: a novel synthesis of 4-iododihydropyrans

The silylated secondary homopropargylic alcohols undergo smooth coupling with aldehydes in the presence of molecular iodine under mild reaction conditions to produce 4-iododihydropyrans in good yields. This method is highly stereoselective, affording cis-dihydropyrans exclusively.     

The reductive etherification of carbonyl compounds using polymethylhydrosiloxane activated by molecular iodine

Aldehydes and ketones undergo a smooth reductive etherification by polymethylhydrosiloxane (PMHS) in the presence of a catalytic amount of molecular iodine under mild conditions to afford the corresponding symmetrical ethers in excellent yields. This new reagent system (PMHS/I₂) provides a simple and convenient route for the preparation of symmetrical ethers from carbonyl compounds.     

Tandem SN2-Michael addition to vinylogous carbonates for the stereoselective construction of 2,3,3,5-tetrasubstituted tetrahydrofurans

A stereoselective method for the synthesis of substituted tetrahydrofuran derivatives employing a tandem alkylation-Michael addition sequence to vinylogous carbonates is developed. The method could be used to synthesize THFs bearing tertiary ethers. Further, the method is extended to the synthesis of adjacent bis-THFs.