Ultrasound-assisted multicomponent synthesis of heterocycles in water – A review

Ultrasound-assisted multicomponent reactions in water are great implements for the development of bioactive compounds. The methodologies for the synthesis of different heterocyclic molecules have acquired enormous attention. Many such techniques are energy-intensive and associated with hazardous chemicals, solvents, expensive work-ups. Low yields and multi-step schemes generate huge organic waste. Hence, researchers thus focussed on benign and eco-friendly techniques to assemble heterocyclic analogs and drug molecules. The ultrasound-assisted synthesis of the target organic moieties frequently facilitates higher product yields than other methodologies. This review is focused on ultrasound-aided multicomponent reactions for synthesizing varied nitrogen-, oxygen-, and sulfur-containing heterocyclic compounds using water as the solvent. The advantages and limitations with respect to yields and reaction conditions are discussed. This evaluation covered the literature reports from 2014 to date.     

Formal synthesis of 14-membered unsymmetrical bis-macrolactone, (−)-colletodiol

Formal synthesis of 14-membered unsymmetrical bis-macrolactone, (?)-colletodiol was accomplished from homopropargylic alcohol derivative. Building of the two different hydroxy acid fragments from the same intermediate of homoallylic alcohol was particularly advantageous. A Sharpless asymmetric dihydroxylation, homologation of carbon chain, a Pinnick oxidation, and a macrolactonization to assemble the 14-membered macrodiolide were the additional salient features of this convergent synthesis.     

Stereoselective β-mannosylation via anomeric O-alkylation: Formal synthesis of potent calcium signal modulator acremomannolipin A

Stereoselective β-mannosylation has been investigated via cesium carbonate-mediated anomeric O-alkylation of d-mannose-derived lactol with various electrophiles. It was found that electrophiles bearing trifluoromethanesulfonate (triflate) as the leaving group are most reactive. In addition, a highly efficient formal synthesis of potent calcium signal modulator acremomannolipin A has been achieved using this β-mannosylation method.     

A New Formal Total Synthesis of β-Elemenone

A short, stereoselective synthesis of an intermediate in Grieco's synthesis of β-elemenone is described.     

Formal synthesis of（＋）-tashiromine and study toward the total synthesis of（＋）-stemoamide

An effcient formal synthesis of（＋）-tashiromine was achieved by employing an intermolecular asymmetric Mannich-type reaction as the key step.Concurrently,a novel approach toward the total synthesis of（＋）-stemoamide through dyotropic rearrangement of 3,4-cis-b-lactone was also explored.     

Acyl furans from cyclohexane-1,3-diones – A synthesis of hibiscone C

A direct route to acyl furans was developed using dithiane anion addition followed by deprotection/aromatization. This led to an efficient synthesis of hibiscone C.     

A novel synthesis of perfluoroalkylglycine

Perfluoroalkylglycine was obtained through perfluoroalkylation of 2-phenyl-5-etho-xyoxazole using RFI-Na2S2O4 reagent system, followed by acid hydrolysis of the intermediates, 2-phenyl-4-perfluoroalkyl-5-ethoxyoxazole and 2-phenyl-4-perfluoroalkyl-2-oxazolin-5-one.     

Formal synthesis of (−)-stemoamide using a useful epimerization at C-8

The formal synthesis of (?)-stemoamide was achieved starting from l-pyroglutamic acid. The key steps used are the allylation using BF₃·OEt₂, ring closing metathesis, allylic oxidation and a novel epimerization at C8.     

Formal synthesis of berkelic acid: a lesson in α-alkylation chemistry

The full details of our enantioselective formal synthesis of the biologically active natural product berkelic acid are described. The insertion of the C-18 methyl group proved challenging, with three different approaches investigated to install the correct stereochemistry. Our initial Horner-Wadsworth-Emmons/oxa-Michael approach to the berkelic acid core proved unsuccessful upon translation to the natural product itself. However, addition of a silyl enol ether to an oxonium ion, followed by a one-pot debenzylation/spiroketalisation/thermodynamic equilibration procedure, afforded the tetracyclic structure of the berkelic acid core as a single diastereoisomer.     

Formal synthesis of (±)-aplykurodinone-1 through an intramolecular Michael addition

A concise and straightforward formal synthesis of (±)-aplykurodinone-1, a degraded steroid natural product isolated from sea hare Syphonota geographica is described, based on an intramolecular Michael addition. The route also includes an intermolecular Michael addition, a Riley selenium dioxide oxidation, and a Krapcho dealkoxycarbonylation. The relative stereochemistries of key intermediates have been determined through single-crystal X-ray diffraction analysis.     

Formal total synthesis of (±)-estrone via the furano diene approach

We present in this report the development and realization of a novel formal total synthesis of estrone (1) via the Torgov diene (24) by the furano diene approach, first attempted by Woodward in 1937. The core ring structure 16 was established by an acid-mediated regioselective and stereospecific cyclization of the endo-oxabicyclo[2.2.1]heptene derivative 14, which is readily available from the AlCl(3)-catalyzed Diels-Alder cycloaddition of 2-(3-methoxyphenethyl)furan (4) and dimethyl maleate. The mechanistic pathway of this S(N)' type cyclization is discussed, and the earlier perspectives in our preliminary report (Org. Lett. 2004, 6, 1333) are corrected.     

Formal synthesis of (±) —quebrachamine through regio- and stereoselective hydrocyanation of arylallene

This article describes the formal synthesis of quebrachamine based on regio- and stereoselective hydrocyanation of 1,3-disubstituted allenes. Allenyl CC double bonds are effectively discriminated through Ni-catalyzed hydrocyanation and a CN group is utilized as a synthon of piperidine ring. Several steps from HCN adduct afforded known intermediates to quebrachamine.     

A convenient synthesis of 6-demethoxycapillarisin

A convenient and effective method for the synthesis of 6-demethoxycapillarisin was described.The highlight was involved in asimple access to the key intermediate 2-ethylthio-5,7-dimethoxy-4H-chromen-4-one from the inexpensive 2,4,6-trihydroxyacetophenone,using AlCl3 as the demethylation reagent.     

Formal total synthesis of (±)-bisabolangelone by using a radical cyclization

A photoreductive cyclization has been used to synthetize the bicyclic core of (±)-bisabolangelone.     

A novel synthesis of (−)-callicarpenal

Callicarpenal, isolated from the leaves of American beautyberry (Callicarpa americana) and Japanese beautyberry (Callicarpa japonica), exhibits significant mosquito bite-deterring activity and repellent activity against ticks and fire ants. The mosquito bite-deterring activity level of callicarpenal was reported to be similar to that of N,N-diethyl-m-toluamide. The novel synthesis of (?)-callicarpenal reported herein was accomplished by starting from (+)-pulegone. In our original approach, a novel Prins-type cyclization based on Meyer–Schuster rearrangement was featured as a key step.     

Total synthesis of (−)-seimatopolide A

The total synthesis of (?)-seimatopolide A is described in a linear fashion with high yielding steps. The key reactions include Lu’s isomerization, Sharpless asymmetric dihydroxylation and Kita’s macrolactonization.     

A novel synthesis of coumarin derivatives

The chemical behaviors of 3-ethynylcoumarin towards benzyl bromide,diazonium chic ride,hydrogen chloride,ethyl magnesium bromide and its self-coupling are reported.