Synthesis of 1,3-difluoroaromatics in one pot by addition of difluorocarbene from sodium chlorodifluoroacetate to 1,2-substituted cyclobutenes

[formula: see text] The synthesis of 1,3-difluoro-2,4-diphenylbenzene has been accomplished in one step from 1,2-diphenylcyclobutene using the environmentally benign difluorocarbene precursor sodium chlorodifluoroacetate. In addition, the preparation of the previously unknown compound 1,3-difluoro-2,4-di-n-propylbenzene has been accomplished in one step from 1,2-di-n-propylcyclobutene using Seyferth's reagent (Ph-Hg-CF3) and sodium chlorodifluoroacetate.     

The synthesis of 5-amino-v-triazolo[4,5-b] pyridin-7-one (l-deaza-8-azaguanine) and 5-amino-3-(β-D-ribofuranosyl)-v-triazolo[4,5-b] pyridin-7-one (1-deaza-8-azaguanosine)

The synthesis of l-deaza-8-azaguanine has been accomplished via a facile route from pyridine precursors. The site of rihosylation and anomeric configuration of l-deaza-8-azaguanosine and several closely related derivatives was accomplished by cmr and pmr, respectively.     

Enantioselective total synthesis of (-)-zampanolide, a potent microtubule-stabilizing agent

An enantioselective total synthesis of zampanolide has been accomplished using a novel DDQ/Br?nsted acid promoted cyclization as the key reaction. The synthesis features cross-metathesis to construct the trisubstituted olefin and a ring-closing metathesis to form the macrolactone. The final N-acyl aminal formation was stereoselectively accomplished by an organocatalytic reaction.     

Regioselective protection of sugars catalyzed by dimethyltin dichloride

The first catalytic process for protection of hydroxyl groups in sugars has been developed. Highly regioselective protection was accomplished along with high chemical yield. The regioselectivity of the benzoylation was realized as an intrinsic character of sugars based on a stereorelationship among their hydroxyl groups. Furthermore, complete protection of alpha-methyl glucoside and beta-methyl xyloside was accomplished.     

Recent advance in heterocyclic organozinc and organomanganese compounds; direct synthetic routes and application in organic synthesis

A practical synthetic route for the preparation of 2-pyridyl and 3-pyridyl derivatives has been accomplished by utilizing a simple coupling reaction of stable 2-pyridylzinc bromides and 3-pyridylzinc bromides. The organozincs used in this study were easily prepared via the direct insertion of active zinc into the corresponding bromopyridines. The subsequent coupling reactions with a variety of different electrophiles have afforded the corresponding coupling products. Using highly active manganese, a variety of Grignard-type organomanganese reagents have been obtained. The subsequent coupling reactions of the resulting organomanganese reagents with several electrophiles have also been accomplished under mild conditions.     

First enantiospecific total synthesis of the antitubercular marine natural product pseudopteroxazole. Revision of assigned stereochemistry

A concise, enantiospecific synthesis of pseudopteroxazole (3), which had originally been assigned structure 1, has been accomplished starting from S-(-)-limonene. The known cyclohexanone 5 was converted in five steps to the alpha,beta-enone 8 by a modified Robinson annulation. Transformation of 8 to the orthogonally protected amino phenol 11 was accomplished by a new modification of the Wolff-Semmler rearrangement. The synthesis was completed by cationic cyclization to form 14 diastereoselectively and subsequent introduction of the terminal oxazole subunit.     

Catalytic enantioselective pyrrole alkylations of alpha,beta-unsaturated 2-acyl imidazoles

[reaction: see text] Enantioselective additions of pyrroles to alpha,beta-unsaturated 2-acyl imidazoles catalyzed by the bis(oxazolinyl)pyridine-scandium(III) triflate complex (1) have been accomplished. The alpha,beta-unsaturated 2-acyl imidazoles were synthesized in high yields through Wittig olefination. A short, enantioselective synthesis of the alkaloid (+)-heliotridane has been accomplished utilizing this methodology and a 2-acyl imidazole cleavage and cyclization. This methodology was then extended to the one-pot asymmetric synthesis of 2-substituted indoles.     

Total synthesis of Tasimelteon

A simple and efficient approach has been accomplished for the total synthesis of active pharmaceutical ingredient (API) of Tasimelteon which is effective for treatment of non-24-h sleep-wake disorder. Starting from 4-vinyl-2, 3-dihydrobenzofuran, the synthesis involves asymmetric epoxidation, Wittig reaction, reduction of the nitrile group and propionation of the amine. The synthesis was accomplished in four steps in overall 48% yield.     

Enantioselective organocatalytic intramolecular Diels-Alder reactions. The asymmetric synthesis of solanapyrone D

The first direct enantioselective organocatalytic intramolecular Diels-Alder reaction has been accomplished. The use of iminium catalysis has provided a new catalytic strategy for the enantioselective [4 + 2] cycloisomerization of a wide variety of tethered diene-enal systems. The use of imidazolidinones 1 and 2 as the asymmetric catalysts has been found to mediate the enantioselective construction of [4.4.0] and [4.3.0] ring systems. Application of this methodology to the highly efficient asymmetric synthesis of the marine metabolite solanpyrone D has also been accomplished. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. Importantly, this technology has been utilized to execute the first enantioselective, catalytic Type II IMDA reaction.     

Building addressable libraries: site-selective use of Pd(0) catalysts on microelectrode arrays

Site-selective Pd(0)-catalyzed reactions have been developed to functionalize a microelectrode array. Heck, Suzuki, and allylation reactions have all been accomplished. The reactions are compatible with both 1K and 12K arrays and work best when a nonsugar porous reaction layer is used. Suzuki reactions are faster than the Heck reactions and thus require more careful control of the reactions in order to maintain confinement. The allylation reaction requires a different confining agent than the Heck and Suzuki reactions but can be accomplished nicely with quinone as an oxidant for Pd(0).     

An efficient procedure for the oxidation of fluorinated carbinols

The oxidation of di and trifluorocarbinols has been accomplished in high yields using the Dess-Martin periodane oxidant.     

Synthesis of the aminocyclopentitol moieties of the hopanoids of Zymomonas mobilis and 'Anacystis montana'

The first synthesis of the cyclopentitol units in bacterial hopanoids has been accomplished from D-glucosamine and the possible biological activity of the free cyclitols as glycosidase inhibitors has been studied.     

Stereoselective synthesis of 2-azetidinones as cholesterol-absorption inhibitors

The synthesis of two 2-azetidinones possessing powerful cholesterol-absorption inhibition properties has been accomplished by a short and highly stereoselective reaction sequence. The key step is the condensation of the titanium enolate of the easily prepared 2-pyridylthioester (R)-11 with imine 6 which affords the desired β-lactam intermediate in the correct relative and absolute configuration. Conversion to the pharmacologically active compounds is readily accomplished by simple functional group manipulation.     

Redox refunctionalization of steroid spiroketals. Structure correction of ritterazine M

The structure of the North spiroketal moiety of ritterazine M has been corrected from 1a to 1b. This was accomplished by comparison of published spectra of the natural product with five synthetic spiroketal-alcohols. Synthesis of these models was efficiently accomplished by reductive cleavage of the spiroketal and Sharpless asymmetric dihydroxylation of an isopentyl, methyl 1,1-disubstituted olefin, followed by Suarez iodine[III] oxidative spirocyclization of monoprotected 1 degree,3 degree 1,2 diols.     

Asymmetric synthesis of cis-7-methoxycalamenene via the intramolecular Buchner reaction of an α-diazoketone

The asymmetric synthesis of cis-7-methoxycalamenene 1 has been accomplished using the intramolecular Buchner reaction of α-diazoketone 7 as the key step in the synthetic route. Upon reduction of the equilibrating azulenone structure 8, the resulting azulenol 9 rearranges to dihydronaphthalene 10 containing the 6,6-membered bicyclic ring system characteristic of 1, by means of an acid-catalyzed aromatization process. Transformation of 10 to 1 is accomplished through a three-step reaction sequence.     

The synthesis of all of the dimethyldibenzothiophenes and monoethyldibenzothiophenes

The synthesis of all four isomers of the monoethyldibenzothiophenes and all of the sixteen isomers of the dimethyldibenzothiophenes has been accomplished.     

Synthesis of fluorescent long-chain thiols/disulfides as building-blocks for self-assembled monolayers preparation

New symmetrical disulfides together with the corresponding thiols bearing fluorescent end-groups have been synthesized as building-blocks for self-assembled monolayers (SAMs). The synthesis has been accomplished starting from aromatic nitrogen heterocycles in three steps. The conversion of the tosylated intermediate into the final disulfide is accomplished by use of sodium hydrogen sulfide (NaSH). Both products (thiols and disulfides) were isolated and characterized.      

Acid-promoted DNA-cleaving activities and total synthesis of varacin C

The first total synthesis of the antibiotic varacin C has been accomplished. In addition, it has been demonstrated that this antibiotic exhibits potent antitumor activity and is capable of causing efficient DNA cleavage under acidic conditions.     

Synthesis of alkylpyrroles by use of a vinamidinium salt

The synthesis of alkyl-substituted 2-pyrrolecarboxylate esters has been accomplished by the condensation reaction of a symmetrical vinamidinium salt and glycine ester derivatives.     

Facile fabrication of hollow polystyrene nanocapsules by microemulsion polymerization

The fabrication of polymer nanocapsules with tailored dimensions has been accomplished by microemulsion polymerization using different surfactants.