Total synthesis of the novel seco-prezizaane sesquiterpenoid (+)-1S-minwanenone

The first total synthesis of (+)-1S-minwanenone, an archetypical seco-prezizaane sesquiterpene, has been accomplished from a readily available chiral endo-tricyclic synthon following a flexible strategy.     

Enantioselective synthesis of epi-(+)-Sch 642305: observation of an interesting diastereoselection during RCM

In an approach towards the enantioselective total synthesis of the novel bioactive natural product Sch 642305, an unusual diastereoselection during the key RCM reaction, resulted in the synthesis of the 11-epi-isomer of Sch 642305.     

Ultrasound and microwave activated preparation of ZrO2-pillared clay composite: catalytic activity for selective, solventless acylation of 1,n-diols

We herein report for the first time, a new and efficient method using ultrasonic activation for intercalation by ion exchange and microwave heating for formation of zirconium polyoxycationic species in the preparation of ZrO₂-pillared clay composite with improved physico-chemical properties and significant reduction in processing time. Acetic anhydride under solventless conditions with microwave irradiation in the presence of ZrO₂-pillared clay was used for the mono-acylation of diols and alcohols in very good yield.     

Total synthesis of the novel NF-kappaB inhibitor (-)-cycloepoxydon

An enantioselective total synthesis of the novel, biologically active epoxyquinone natural product (-)-cycloepoxydon has been accomplished from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone. A new cycloepoxydon related heptacyclic dimer has been prepared and characterized. [reaction: see text]     

Synthetic studies toward geranylated PPAP natural products oblongifolin A, oblongifolin D, and enervosanone

A concise approach of general utility toward mono- and di-geranylated PPAP frameworks employing ‘reconstructive aldol cyclization’ as the key step is delineated.     

Towards the total synthesis of neurotrophically active tashironins: rapid construction of the tetracyclic core through a tandem oxidative dearomatization-IMDA reaction-RCM protocol

An exceptionally short (three step) strategy involving tandem oxidative dearomatization, intramolecular Diels-Alder (IMDA) reaction and RCM has been devised to generate the complete carbon framework present in tashironin-type sesquiterpenoid natural products.     

Construction of the 3-prenyl-4-oxa-tricyclo[4.3.1.0]dec-8-en-2-one core of caged xanthonoid natural products via tandem Wessely oxidation-intramolecular [4+2] cycloaddition

A two-step protocol based on tandem Wessely oxidation/intramolecular Diels-Alder reaction to provide general access to the 3-prenyl-4-oxa-tricyclo[4.3.1.0^3,7]dec-8-en-2-one core present in the caged Garcinia xanthonoids is demonstrated. These readily accessible tricyclic scaffolds also provide ready entry into a variety of substituted γ-lactones through a photochemical 1,3-acyl shift and decarbonylation.     

Unprecedented chemical transformation of semicarbazones mediated by Wilkinson's catalyst

para-Nitrobenzaldehyde semicarbazone undergoes an unusual chemical transformation upon reaction with [Rh(PPh(3))(3)Cl] in the presence of trialkyl and dialkylamines (NR(2)R'; R = Et,(i)Pr, (n)Bu; R' = H or R' = R) via dissociation of the C-NH(2) bond and formation of a new C-NR(2) bond (where the NR(2) fragment is provided by the amine). The transformed semicarbazone ligand binds to rhodium as a dianionic C,N,O-donor to afford complexes of type [Rh(PPh(3))(2)(CNO-NR(2))Cl] (CNO-NR(2) = the coordinated semicarbazone ligand). Another group of semicarbazones (viz. salicylaldehyde semicarbazone, 2-hydroxyacetophenone semicarbazone, and 2-hydroxynaphthaldehyde semicarbazone) has also been observed to undergo a similar chemical transformation upon reaction with [Rh(PPh(3))(3)Cl] under similar experimental conditions as before, and these transformed semicarbazones bind to rhodium as dianionic O,N,O-donors affording complexes of the type [Rh(PPh(3))(2)(ONO(n)-NR(2))Cl] (ONO(n)-NR(2) = the coordinated semicarbazone ligand; n = 1-3). The structure of the [Rh(PPh(3))(2)(CNO-NEt(2))Cl] and [Rh(PPh(3))(2)(ONO(2)-NR(2))Cl] complexes has been determined. All the complexes show characteristic (1)H NMR signals. They also show intense absorptions in the visible and ultraviolet region. Cyclic voltammetry on the complexes shows an oxidative response within 0.52-0.97 V versus SCE and a reductive response within -1.00 to -1.27 V versus SCE, where both the responses are believed to be centered on the semicarbazone ligand.     

Total synthesis of epi-otteliones

[reaction: see text] Syntheses of 6-epi- and 8-epi-otteliones, corresponding to earlier proposed structures of the biologically potent natural product ottelione A, have been accomplished from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone.