The Carbon Zip Reaction: A Method for Expanding Carbocycles

A general method for enlargement of carbocyclic rings by the so called zip reaction is given. The Michael adducts of 2-nitrocycloalkanones with 3-oxo-4-pentenoates in the presence of tetrabutylammonium fluoride give in high yield compounds with the ring enlarged by four C-atoms. By this method 7-, 8-, and 12-membered cycloalkanones were converted respectively to 11-, 12-, and 16-membered functionalized carbocycles (see Scheme 2 and 3).     

Enhanced phosphorescence in intramolecular exciplex systems

Phosphorescence behavior of the series of compounds, (carbazole)-(CH₂)_n-(terephthalic acid methyl ester), which show intramolecular exciplex emission, has been studied in a rigid medium at 77 K. The phosphorescence of the carbazole moiety is enhanced by electron transfer fluorescence quenching of the carbazole residue in accord with the degree of quenching.     

Stereoselective synthesis of highly enantioenriched (E)-allylsilanes by palladium-catalyzed intramolecular bis-silylation: 1,3-chirality transfer and enantioenrichment via dimer formation

Highly enantioenriched (E)-allylsilanes have been synthesized from optically active allylic alcohols on the basis of Pd-catalyzed intramolecular bis-silylation followed by highly stereospecific Si-O elimination reactions. The method involves three steps: 1) O-disilanylation of the allylic alcohols with chlorodisilanes, 2) intramolecular bis-silylation in the presence of a 1,1,3,3-tetramethylbutyl isocyanide/[Pd(acac)2] (acac = acetylacetonate) catalyst at 110 degrees C, and 3) treatment of the reaction mixture with organolithium reagents. The overall transformation proceeds with nearly complete conservation of the enantiopurity of the starting allyl alcohols by transposition of the C=C bond. For instance, (R)-(E)-3-decen-2-ol (99.6-99.7 % ee) produced (S)-(E)-4-(organosilyl)-2-decene of 98.8-99.4 % ee for a variety of silyl groups, including Me3Si, Me2PhSi, tBuMe2Si, Et3Si, and iPr3Si. In the bis-silylation step, the initially formed trans-1,2-oxasiletanes immediately dimerize to stereoselectively give 1,5-dioxa-2,6-disilacyclooctanes, which are isolated in high yield by carrying out the reaction at 70 degrees C. The eight-membered ring compounds undergo thermal extrusion of (E)-allylsilanes in high yield at 110 degrees C, along with formation of 1,3-dioxa-2,5-disilacyclohexane derivatives. These in turn undergo a Peterson-type elimination by treatment with nucleophiles such as BuLi and PhLi to give the (E)-allylsilanes. All of the steps involved in the sequence proceed with extremely high stereoselectivity and stereospecificity, leading to almost complete 1,3-chirality transfer through the overall transformation. The dimerization step, which forms diastereomeric intermediates, allows the synthesis of a highly enantioenriched allylsilane (99.4 % ee) from an optically active allylic alcohol with lower enantiopurity (79.2 % ee) by enrichment of enantiopurity. A general method for the determination of the enantiomeric excesses of (E)-allylsilanes is also described in detail.     

Syntheses of (1,1-dihydroperfluoroalkyl)aryliodonium triflates and their analogues

(1,l-Dihydroperfluoroalkyl)phenyl- and -$\text{p}$-fluorophenyliodonium triflates $\text{2}$ and $\text{3}$ were synthesized by the reaction of l-bis(trifluoroacetoxy)iodo-1,l-dihydroperfluoroalkanes $\text{1}$ with triflic acid and benzene or fluorobenzene in 1,1,2-trichlorotrifluoroethane. The use of fluorosulfonic acid and sulfuric acid instead of triflic acid afforded (1,l-dihydroperfluoroalkyl) phenyliodonium fluorosulfonate $\text{4}$ and sulfate $\text{5}$, respectively. Similarly, (1,1,ω-trihydroperfluoroalkyl)phenyliodonium triflate $\text{7}$ and 1,1,5,5-tetrahydroperfluoropentane-l,5-bisphenyliodonium triflate $\text{9}$ were synthesized.     

Substitution and elimination reactions of poly(epichlorohydrin) and poly(2-chloroethyl vinyl ether) using phase transfer catalysis

The reactions of poly(epichlorohydrin) (PECH) and poly(2-chloroethyl vinyl ether) (PCEVE) with various reagents were investigated using phase transfer catalyst (PTC) such as tetra-n-butylammonium bromide (TBAB), 18-crown-6 (CR6), and dicyclohexyl-18-crown-6 (DCHC) is a solid—liquid two-phase system. Although the reactions of these polymers hardly occurred without PTC in nonpolar solvents such as toluene and diglyme under mild conditions, the addition of PTC caused the reactions to proceed smoothly under the same conditions. In addition, the reactions of PECH and PCEVE with a strong base such as potassium hydroxide proceeded selectively through β-elimination reaction to produce the polymers with pendant vinyl groups. These results suggested this method is useful for the syntheses of functional polymers. On the other hand, it turned out that quaternary ammonium salts such as TBAB have higher catalytic activity than crown ethers such as CRG and DCHE in these reactions. Furthermore, the catalytic activity of quaternary ammonium salts was strongly influenced by their chain length and the structure of the polymers.     

One-pot sequential four-component coupling via Cp*RuCl-catalyzed cyclotrimerization and Suzuki-Miyaura coupling

The catalytic intermolecular cyclotrimerization of alkynylboronates, propargyl alcohols, and terminal alkynes was accomplished by means of the ruthenium catalysis and the temporary tethering approach with the C-B-O linkage to give rise to highly substituted arylboronates with excellent selectivity. The resultant arylboronates were further converted to highly substituted biaryls via the Suzuki-Miyaura coupling with various aryl iodides using Pd₂(dba)₃/PCy₃ as a catalyst precursor in aqueous toluene. As a consequence, the four-component coupling approach to highly substituted biaryls was successfully established by combining these two operations into a sequential one-pot process.     

Asymmetric conjugate reduction of alpha,beta-unsaturated ketones and esters with chiral rhodium(2,6-bisoxazolinylphenyl) catalysts

New asymmetric conjugate reduction of beta,beta-disubstituted alpha,beta-unsaturated ketones and esters was accomplished with alkoxylhydrosilanes in the presence of chiral rhodium(2,6-bisoxazolinylphenyl) complexes in high yields and high enantioselectivity. (E)-4-Phenyl-3-penten-2-one and (E)-4-phenyl-4-isopropyl-3-penten-2-one were readily reduced at 60 degrees C in 95 % ee and 98 % ee, respectively, by 1 mol % of catalyst loading. (EtO)2MeSiH proved to be the best hydrogen donor of choice. tert-Butyl (E)-beta-methylcinnamate and beta-isopropylcinnamate could also be reduced to the corresponding dihydrocinnamate derivatives up to 98 % ee.     

Medicinal flowers. VIII. Radical scavenging constituents from the flowers of Prunus mume: structure of prunose III

The methanolic extract and its fractions from the fresh flowers of Prunus mume SIEB. et ZUCC. were found to show scavenging effects on 1,1-diphenylpicryl-2-hydrazyl (DPPH) radical and superoxide. The fragrance constituents of P. mume were analyzed by GC-MS and a new polyacylated sucrose, prunose III, was isolated from the ethyl acetate-soluble fraction. The structure of prunose III was determined on the basis of chemical and physicochemical evidence as 4,3',4',6'-tetra-O-acetyl-6-O-p-coumaroylsucrose. In addition, the scavenging effects of the principal constituents on DPPH radical and superoxide were examined.     

Kinetic comparisons of anthocyanin reactivities towards 2,2'-azobis(2-amidinopropane) (AAPH) radicals, hydrogen peroxide and tert-buthylhydroperoxide by capillary zone electrophoresis

Twelve major anthocyanins identified in bilberry extracts were studied in vitro using capillary zone electrophoresis (CZE) for their reactions towards 2,2'-azobis(2-amidinopropane) (AAPH) radicals, hydrogen peroxides (H(2)O(2)) and tert-buthylhydroperoxides (t-BuOOH). Reactivity towards AAPH radicals was primarily determined by the aglycon structure, not by the type of sugar moiety. Delphinidins carrying three-hydroxyl groups on the B ring were most reactive followed by cyanidins, with two-hydroxyl groups. Further, methylation of the hydroxyl groups reduced reactivity towards AAPH radicals. However, reactivity of anthocyanins towards H(2)O(2) was not significantly affected by aglycon structure or by the type of sugar moiety; there being no marked difference in reaction rates among the anthocyanins. Reactivity towards t-BuOOH was essentially the same as towards H(2)O(2), although the reaction rate was several times smaller. Also, the reaction rate of anthocyanin towards peroxide was relatively high compared to that of (+)-catechin (approximately 30 times larger) measured as a reference antioxidant, whereas the reactivities of anthocyanins and (+)-catechin towards AAPH radicals were similar.     

Asymmetric reduction of alkyl phenyl ketones with a chiral hydride reagent prepared from lithium aluminum hydride and (S)-4-anilino-3-methylamino-1-butanol

The asymetric reduction of alkyl phenyl ketones with a chiral hydride reagent derived from lithium aluminum hydride and (S)-4-anilino-3-methylamino-1-butanol, which is prepared from (S)-aspartic acid, gives (S)-alkylphenylcarbinols in high chemical and optical yields.