An extraordinarily rapid polymerization of vinylpentafluorocyclopropane: highly stereo- and regioselective synthesis of unsaturated fluoropolymers

Vinylpentafluorocyclopropane 1 was prepared from the reaction of 1,1,2-trifluoro-4-bromobutene and hexafluoropropylene oxide at 190 degrees C, following by treatment with KOH. 1 is stable at low temperature (-40 degrees C) for 7 years, but it rearranged readily to 2,3,3,4,4-pentafluorocyclopentene-1, 2, at above 80 degrees C (Ea = 28.7 kcal/mol). Under radical conditions, 1 extraordinarily rapidly polymerizes to give highly crystalline Z-fluoropolyolefin (CF2CF2CF=CHCH2)n, 3, which is very useful for cross-linking and grafting but difficult to obtain by other means. The stereochemistry of 3 was further confirmed by radical addition of iodine to 1 to form Z-ICF2CF2CF=CHCH2I, 4, exclusively. The rapid polymerization with high stereoselectivity and regioselectivity could be rationalized by effects of a favorable polar transition state of a high ring strain and electron-deficient pentafluorocyclopropyl and a relative electron-rich double bond of 1.     

Electrophile-driven regioselective synthesis of functionalized quinolines

Highly substituted 3-iodoquinolines bearing different alkyl and aryl moieties can be synthesized in moderate to excellent yields (up to 99%) by 6-endo-dig iodocyclization of 2-tosylaminophenylprop-1-yn-3-ols with molecular iodine (I(2)) under mild conditions. The cyclization is highly regioselective and the resulting 3-iodoquinolines can be further functionalized by various coupling reactions.     

Easy and regioselective synthesis of highly functionalized o-quinodimethide precursors from Fischer carbene complexes and isocyanides

Highly functionalized cis- and trans-1,2-bis(trialkylsilyloxy)benzocyclobutene derivatives have been synthesized in a completely regioselective fashion from easily available Fischer alkenylcyclobutenyl(alkoxy)carbene complexes and isocyanides. This methodology can be viewed as an alternative to existing methods of synthesis of this kind of compounds and overcomes the main problem of introducing functionality in the aromatic ring. Both cis and trans derivatives underwent the expected fragmentation to generate o-quinodimethide intermediates upon thermal treatment, affording complex polycyclic structures in a stereoselective manner when heating was carried out in the presence of a range of electron deficient dienophiles.     

Regio- and stereoselective synthesis of highly functionalized vinyl ethers via coiodination of acetylenic ketones

A Cu(OTf)₂-catalyzed highly regio- and stereoselective coiodination of acetylenic ketones was reported, providing a mild and convenient method for the synthesis of (Z)-β-carbonyl-β-iodoenol ethers in good yields.     

A highly regioselective tandem 1,3-dipolar cycloaddition of cyclopropene 1,1-diesters and nitrile oxides: synthesis of highly functionalized isoxazoles

A highly regioselective tandem 1,3-dipolar cycloaddition of cyclopropene 1,1-diesters with nitrile oxides was described. This reaction supplied a new method for synthesis of polyfunctionalized isoxazole derivatives in moderate to excellent yields under mild conditions.     

Angular hydroxymethyl directed intramolecular Diels-Alder approach for the stereo- and regioselective synthesis of pimaraditerpenes

The stereo- and regioselective synthetic route to pimaraditerpenes, employing an angular hydroxymethyl directed intramolecular Diels-Alder reaction of the decaline intermediate, has been developed. This synthetic approach allows prompt access to both natural pimaraditerpenes and the unnatural regioisomers, which would be potentially new anti-inflammatory pimaraditerpenes.     

Photoelectron spectra of vinyl tellurides

The lowest energy band in the photoelectron (PE) spectra of alkyl vinyl tellurides is attributed to-MO with predominant contribution from the p_z-AO of the tellurium atom. The second and fourth lowest energy bands correspond to-MO. An additional-MO is located between these-MO. The introduction of a second vinyl group hardly affects the HOMO. The heterocyclization of divinyl telluride has a large perturbation effect. Nevertheless, divinyl telluride and tellurophene have the same type of orbital structure.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 935–939, April, 1991.     

Facile synthesis of highly functionalized ethyltrifluoroborates

Organotrifluoroborates are generating increased interest because of their ease of preparation and purification and indefinite shelf life. Herein we report the preparation of organotrifluoroborates bearing functional groups that can be manipulated at different stages of the synthetic route, exploiting the inertness of their carbon-boron bonds. The alkylation of 2,2-dicyanoethyltrifluoroborate with a variety of electrophiles and of (EWG)2CH2 with potassium iodomethyltrifluoroborate resulted in di- and trisubstituted ethyltrifluoroborates in good to excellent yields.     

Phosphine-catalyzed synthesis of highly functionalized coumarins

2-Styrenyl allenoates are converted into cyclopentene-fused dihydrocoumarins through phosphine-catalyzed regio- and diastereoselective [3 + 2] cycloadditions. Remarkably, changing the solvent from THF to benzene promotes the conversion of the 2-(2-nitrostyrenyl) allenoate into a tricyclic nitronate through a previously undocumented mode of phosphine catalysis. This nitronate was subjected to efficient face-, regio-, and exo-selective 1,3-dipolar cycloadditions to provide tetracyclic coumarin derivatives.     

Ligand-modulated stereo- and regioselective tandem addition reactions of rhenium-bound naphthalene

A series of complexes of the form TpRe(CO)(L)(eta(2)-naphthalene) (Tp = hydridotris(pyrazolyl)borate) undergoes tandem electrophile/nucleophile addition reactions with a high degree of regiocontrol depending on the auxiliary ligand, L. When L = PMe(3), the reaction of the eta(2)-naphthalene complex with triflic acid followed by a silyl ketene acetal favors the 1,4-addition product, whereas when L = pyridine, N,N-dimethylaminopyridine, N-methylimidazole, or NH(3) the 1,2-addition product is favored. These reactions proceed with excellent stereocontrol: both electrophile (H(+), D(+)) and nucleophile (silyl ketene acetal) add anti to the face of metal coordination, and a single coordination diastereomer can be isolated for each reaction. One-electron oxidation of the Re complex affords the corresponding free dihydronaphthalene in good yield.     

L-ProT catalyzed highly regioselective N-alkoxyalkylation of purine rings with vinyl ethers

An efficient and regioselective synthesis of N-9 alkoxyalkylated purine nucleoside derivatives was achieved via the N-alkoxyalkylation of purine rings with vinyl ethers catalyzed by L-ProT.The advantages of this protocol include good to excellent yield,mild reaction condition,and simple manipulation.A plausible mechanism for the transformation was given.     

A domino-based approach toward stereodefined heavily functionalized cyclohexanes: synthesis of iridal's core structure

A stereoselective synthesis of heavily functionalized six-membered ring subunits, which possess functionality at sites appropriate for further elaboration, is described. The cyclopentanone moiety of hydrindenediol is required to achieve total facial selectivity during the pre-domino installation of the second quaternary center, while oxidative cleavage is responsible for the ring-expanding rearrangement. A microwave-assisted version of the key domino transformation and a test of concept approach toward the iridal core structure are also presented.     

LiClO4-Activated stereo- and regioselective alkylation of aldehydes

Aldehydes undergo an unusual and very mild alkylation by LiClO₄-activation in the presence of acids. This new methodology enables the inclusion of a broad range of aldehydes as well as tertiary alcohols. Regio- and stereoselectivity observed during this reaction will be discussed.     

Efficient synthesis of highly functionalized cyclic aminimides

[reaction: see text]. Simple condensation reactions of various alpha,beta-epoxy or alpha,beta-aziridinyl methyl esters with 1,1-dialkyl hydrazines provided cyclic aminimides (1,1-dialkyl-3-oxopyrazolidines) with a heteroatom substituent at the 4-position in good yields. The reaction proceeds smoothly, without any coreagent, providing the product as an easily isolable precipitate. The reaction is expected to be a good candidate for combinatorial synthesis of a highly functionalized five-membered ring scaffold. The scope and limitations of this reaction were investigated by varying the substituents R(1)-R(5).     

Stereocontrolled synthesis of highly functionalized spirocyclic pyrans

Highly functionalized spirocyclic pyrans can be obtained through the Achmatowicz rearrangement of furyl carbinols by taking advantage of the different rates of reaction for epoxidation and nucleophilic addition. Through this methodology, spirocyclic units of various ring sizes can be selectively generated with complete stereocontrol.     

Palladium-catalyzed regioselective synthesis of benzosultams from functionalized ynamides and benzotriazoles/tetrazoles

Palladium-catalyzed highly regioselective synthesis of benzotriazole appended benzosultams by the tandem-cyclization of functionalized ynamides with benzotriazoles has been accomplished. This transformation involves the formation of both CN and CC bonds in a single step. Donor solvents appear to enhance the yields of the products. The methodology is also applicable for the generation of triazole/tetrazole appended benzosultams.