Efficient synthesis of functionalized pyrimidones via microwave-accelerated rearrangement reaction

An efficient synthesis of functionalized pyrimidones via microwave-accelerated rearrangement reaction of amidoxime DMAD adducts is described. In most cases, the pyrimidone formation was furnished in reasonable yield after 2 min of microwave irradiation.     

Convergent synthesis of fully functionalized ring C allocolchicinoids. Benzannulation approach

[reaction: see text]. A novel convergent approach to fully functionalized ring C allocolchicinoids is developed which is based on the benzannulation reaction of Fischer carbene complexes with alkynes. The efficacy of this strategy was established with the conversion of bromide 1a (R1 = Me, R2 = H) to the biaryl phenol 3a (R = Me, R(L) = Pr, R(S) = H) via the carbene complex 2a. Bromide 1b (R1 = t-Bu, R2 = OMe) was then used for the analogous preparation of the diastereomeric allocolchicinoids 3b (R = Me, R(L) = Pr, R(S) = H).     

Studies on histionicotoxin: rearrangement of the spirocyclic histrionicotoxin carbon skeleton into the fused pumiliotoxin skeleton

On treatment with acid the spirocyclic ketoamine $\text{5}$ undergoes a retro-Mannich reaction followed by recondensation to give the unsaturated imine $\text{8}$, thus converting the histrionicotoxin carbon skeleton into the pumiliotoxin C skeleton.     

The pyrrole approach toward the synthesis of fully functionalized cup-shaped molecules

[reaction: see text] A novel method for the synthesis of new highly functionalized cyclotrimers is described. The method consists of an original synthesis of beta-dibromosubstituted pyrroles, metalation, cycloaddition, and cyclotrimerization. The sequence is highly compatible with common functional groups and allows the construction of cup-shaped molecules functionalized both at the upper and bottom rim. This feature makes the newly formed structures useful scaffolds for the development of supramolecular receptors.     

Efficient quenching of photoluminescence from functionalized single-walled carbon nanotubes by nitroaromatic molecules

The photoluminescence from functionalized single-walled carbon nanotubes was found to be highly sensitive to the presence of nitroaromatic compounds such as nitrobenzene, 4-nitrotoluene, and 2,4-dinitrotoluene. The strong luminescence quenching in solution was at the upper limit of diffusion-control and also showed significant static quenching contributions. Mechanistic implication of the results and potential applications are discussed.     

Chiron approach to fully functionalized cyclohexane frame of (+)-Resiniferatoxin

The commercially available (−)-Shikimic acid is used to construct the fully functionalised cyclohexane frame (C-ring) of (+)-Resiniferatoxin. The key reactions involve stereo-selective epoxide opening with trimethylaluminium and vinyl Grignard reaction.     

Favorskii rearrangement of a highly functionalized meso-dihaloketone

This paper describes studies on the feasibility of an asymmetric Favorskii rearrangement of a meso-dihaloketone substrate. In the racemic series, metal amide bases in the presence of amines give poor to reasonable yields of ring-contracted unsaturated cyclopentyl amides, whilst amines in aqueous solvent mixtures afford cyclopentyl amides in good to excellent yields. A range of chiral non-racemic amines are screened, a tiny diastereo-bias is observed and a tentative mechanistic rationale for the diastereoselective process is proposed.     

An expedient approach to internally functionalized chiral dendrimers: synthesis of a dendritic molecule incorporating furanoside skeleton

In an approach to chiral dendritic molecules, a dendrimer incorporating pentose units in the interior and hexose units in the periphery is built up on a 1, 3, 5-trisubstituted aromatic core by using 1,2:5,6-diisopropylidene glucose as the carbohydrate precursor and a 3, 5-disubstituted aromatic unit as the branching block. The carbohydrate moiety also provides internal functionalities in the form of hemiacetal moiety of the furanoside ring.     

Thermal rearrangement of divinylcyclopropane systems. Preparation of functionalized,stereochemically defined bicyclic and tricyclic products containing the bicyclo[3.2.1]octane skeleton

A study involving the preparation and thermolysis of substituted 6-$\text{exo}$-(1-alkenyl)bicyclo[3.1.0]hex-2-ene systems (14, 15, 23, 29, 40) shows (a) that C-8 functionalized bicyclo[3.2.1]octa-2,6-dienes can be prepared readily $\text{via}$ this methodology (14 → 16; 15 → 17), (b) that the rearrangement reaction is stereospecific even when the 6-(1-alkenyl) group is substituted with a sterically bulky isopropyl group (23 → 24; 29 → 30), and (c) that the method can be extended to include the preparation of tricyclic systems (40 → 41).     

Synthesis of the forskolin skeleton via anionic oxy-cope rearrangement

The forskolin prototype 14 has been elaborated in 9 steps from 2,4,4-trimethylcyclohexenone (5), the entire ring system materializing during oxyanionic Cope rearrangement of alcohol 10.     

Efficient access to 5-substituted thiazoles by a novel metallotropic rearrangement

A novel rearrangement process involving the migration of trimethylstannanyl or trimethylsilanyl groups around the thiazole ring provides access to either 2- or 5-metallated thiazoles by tuning the reaction conditions. The proposed mechanism, based on experimental evidence, is characterized by the catalytic role of thiazole bisadducts as metal-transfer agents.     

A novel rearrangement of eudesmanolide enol ester epoxide: facile 1-step construction of the salvialane sesquiterpene skeleton

A novel carbon–carbon rearrangement for the eudesmanolide sesquiterpene enol ester epoxide in the presence of a catalytic amount of Lewis acids (3–10 mol%) or an excess of NaOMe is disclosed. This reaction was developed to give a facile, one-step procedure for the construction of naturally occurring and bioactive salvialane sesquiterpenes. The reaction conditions were investigated extensively and a possible reaction mechanism is also discussed.     

An unexpected rearrangement of the benzofurobenzazepine skeleton of galanthamine-type alkaloids

Attempted cyclisation of N-methylated spiro benzazepine-cyclohexenone (5) into the corresponding N-methyl tetracyclic unit of galanthamine-type alkaloids (6) instead gave an unexpected rearrangement to yield a cyclopentanoisoquinolinone derivative (7). Methylation of the tetrahydrobenzofurobenzazepine tetracycle resulted in the expected N-methyl derivative 6, and the anomalous product 8, with structure similar to that of 7.     

Synthesis of a pladienolide B analogue with the fully functionalized core structure

Starting from (R)-(-)-linalool (6), terminus differentiation and chain extension via aldol type reactions led to ketophosphonate 16 (C1-C8 building block). In a Horner-Wadsworth-Emmons reaction, 16 reacted with aldehyde 22, which contained the vicinal anti-Me-OH pattern and a vinyl iodide function, to provide the C1-C13 part of pladienolide B. After Shiina macrolactonization, reduction of the enone 26 gave the core structure 27. A Stille cross-coupling of vinyl iodide 27 with tributylphenylstannane eventually furnished analogue 30.     

Efficient synthesis of highly functionalized tetrahydropyridopyrimidines by a novel three-component coupling reaction

We report the development of a novel three-component coupling reaction (3CC) for the synthesis of alkoxy tetrahydropyridopyrimidines. Systematic optimization of reaction parameters identified 3CC conditions tolerant of a wide array of functionality at all three sites of diversity, providing densely functionalized products in moderate to excellent yields. The newly developed chemistry has since been applied to the lead optimization process on a novel drug discovery program, facilitating rapid compound advancement.     

On the use of epoxy alcohol-aldol rearrangement for stereoselective construction of quarternary carbon centers

A new method for the construction of quarternary carbon centers is reported, which is based on the Lewis acid-promoted 1,2-rearrangement of β,γ-epoxy alcohols giving α,α-disubstituted aldols stereospecifically in high yields.     

Photochemical approach toward deposition of gold nanoparticles on functionalized carbon nanotubes

The development of new methods for the facile synthesis of hybrid nanomaterials is of great importance due to their importance in nanotechnology. In this work, we report a new method to deposit Au nanoparticles on the surface of single-walled carbon nanotubes (SWCNTs). Our approach consists of a one pot synthesis in which Au nanoparticles are generated in the presence of a photoreducing agent (Irgacure-2959) and carboxyl or polymer-functionalized SWCNTs (f-SWCNTs). We have observed that when carbon nanotubes are functionalized with polymers containing pendant amino groups, the latter can act as specific nucleation sites for well-dispersed deposition of Au nanoparticles. The surface coverage of the Au nanoparticles can be observed by transmission electron spectroscopy. These observations are compared to that of carboxyl functionalized SWCNTs, in which less surface coverage was observed. The f-SWCNT/Au nanocomposites were also characterized by UV-vis, infrared, and Raman spectroscopy and thermogravimetric analysis (TGA). This facile and effective route can be implemented to deposit gold nanoparticles on other surface-functionalized carbon nanotubes.     

Novel approach for the stereocontrolled construction of eudesmane skeleton: a concise synthesis of (+/-)-balanitol

[structure: see text] A novel method for the stereocontrolled construction of the eudesmane ring system based on a cationic cyclization is presented, and the approach is exemplified in a short and efficient total synthesis of (+/-)-balanitol (2).