Synthesis of cyclopent[bindoles by formal [3+2]-addition of indolylmethyl cations to alkenes

Treatment of indole-2- or 3-methanols with tin(IV) chloride as Lewis acid in the presence of styrenes results informal [3+2]-addition of the indole stabilised cation to the alkene to give cyclopent[b]indoles with a high degree of stereoselectivity; use of methylcyclohexene as the alkene component gave the cis-fused cyclopent[b]indole 17, which was independently synthesised in enantiomerically pure form from the diketone 18.     

Radiotracer studies on calcium ion-selective electrode membranes based on poly(vinyl chloride) matrices

Radiotracer studies with ⁴⁵Ca and ³⁶Cl demonstrate that PVC matrix membranes containing Orion 92-20-02 liquid calcium ion-exchanger are permselective to counter-cations. Diffusion coefficients are quoted for the migration of ⁴⁵Ca between pairs of calcium solutions and are discussed in terms of solution concentration, membrane thickness and concentration level of sensor in the membrane. Migration of calcium ions from calcium chloride solution to a Group (II) metal chloride solution through a PVC membrane containing calcium liquid ion-exchanger is discussed in terms of solvent extraction and electrode selectivity coefficient parameters. Thus, magnesium, strontium and barium ions appear to inhibit migration through the membrane by their low affinity for the membrane liquid ion-exchanger sites, while the inhibition by beryllium ions is attributed to site blockage by the strong affinity of dialkylphosphate sites for beryllium.     

Interference studies on a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate as sensor and tri-n-pentyl phosphate as solvent mediator

Interference potentials, E(M), defined as the difference between the observed potential and the potential calculated assuming that there is no interference, have been determined, and their fit to the equation E(M) = -(RT/F) 1n [1 + K(M)a(B)/(a(Ca))1 2 (z(B)) discussed for a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate as sensor with tri-n-pentyl phosphate as solvent mediator in mixed solutions of CaCl(2)BCl(x), where B = Li, Na, K, Mg, Zn or Cu, at total ionic strengths of 0.2, 0.4 and 0.6. Generally, K(M) for the alkali metal ions is considerably less for this electrode than for a comparison electrode based on Orion 92-20-02 liquid ion-exchanger in PVC. Occasionally, the data do not fit the equation. Thus, particularly for the bivalent ions, although the plots of exp[-E(M)F/RT] vs. a(B)/(a(Ca))1 2 (z(B)) are usually linear, they frequently do not intercept the ordinate at 1.00 and/or may give negative slopes and hence negative K(M) values.     

Chiral oxime ethers in asymmetric synthesis. O-(1-Phenylbutyl)benzyloxyacetaldoxime, a versatile reagent for the asymmetric synthesis of protected 1,2-aminoalcohols, alpha-amino acid derivatives, and 2-hydroxymethyl nitrogen heterocycles including iminosugars

Addition of a range of organolithium and Grignard reagents to (E)-O-(1-phenylbutyl)benzyloxyacetaldoxime 1 in the presence of boron trifluoride diethyl etherate is highly diastereoselective. The resulting hydroxylamines undergo N-O bond cleavage upon treatment with zinc-acetic acid or molybdenum hexacarbonyl to give, after N-protection, protected 1,2-aminoalcohols 3 in high enantiomeric purity. Debenzylation of 3a and 3d gave N-Boc (R)-alaninol and (S)-phenylalaninol respectively. The hydroxylamines 2 also serve as alpha-amino acid precursors, 2i being converted into N-formyl-(R)-alaninyl-(S)-(4-bromo)phenylalanine ester 7, the N-terminal dipeptide of a natural depsipeptide. The versatility of the 1,2-aminoalcohol derivatives was further illustrated by their conversion into 5-, 6- and 7-membered 2-hydroxymethyl nitrogen heterocycles 15-19 in high enantiomeric excess by a ring-closing metathesis reaction. Further reaction of the dihydropyrrole 15 gave the iminosugar 1,4-dideoxy-1,4-imino-D-ribitol.     

N-H Insertion reactions of rhodium carbenoids. Part 5: A convenient route to 1,3-azoles

Dirhodium(II) carboxylate catalysed reaction of diazocarbonyl compounds 2 in the presence of primary amides 1 results in the formation of α-acylaminoketones 3 (12 examples) by N-H insertion reaction of the intermediate rhodium carbene. The 1,4-dicarbonyl compounds 3 are readily converted into structurally diverse oxazoles 4 (11 examples) by cyclodehydration, thiazoles 5 (10 examples) by treatment with Lawesson's reagent, or imidazoles 6 (2 examples) by reaction with ammonia or methylamine.