Synthesis of 2-substituted benzofurans and indoles using functionalized titanium benzylidene reagents on solid phase

Titanium(IV) benzylidenes bearing a masked oxygen or nitrogen nucleophile in the ortho position were generated from thioacetals, using low-valent titanocene complex, Cp2Ti[P(OEt)3]2. Methylene acetal, alkyl ether, silyl ether, fluoro, tertiary amino, and N-alkyl, N-benzyl, N-prenyl, and N-silyl tert-butyl carbamate groups were tolerated in the titanium alkylidene reagents (Schrock carbenes). Aryl-chlorine bonds were stable to the titanium benzylidene functionality, but there was poor chemoselectivity for the reduction of the thioacetal in the presence of an aryl chloride. The titanium benzylidenes converted Merrifield and Wang resin-bound esters into enol ethers. The oxygen nucleophile was masked as a TMS ether, and when the resin-bound enol ethers bearing this ortho substituent were treated with 1% TFA in dichloromethane, benzofurans were released from resin in high yields. The chameleon catch strategy ensured excellent purity. In a similar way, N-alkylated and N-silylated tert-butyl carbamates were used for the synthesis of N-alkyl and N-Boc indoles, respectively. These traceless solid-phase syntheses of heterocycles are believed to involve postcleavage modification rather than cyclative termination.     

In situ ammonia generation as a strategy for catalytic NOx reduction under oxygen rich conditions

Under highly oxygen rich conditions palladium/alumina catalysts exhibit strongly enhanced NOx reduction activity in the presence of CO:H2 mixtures due to in situ generation of ammonia via the formation and subsequent hydrolysis of isocyanate (NCO) species.     

A comparison of algorithms for polynomial interpolation

Eight different algorithms for polynomial interpolation are compared with respect to stability and computational efficiency. Large differences in performance are described and certain methods are shown to be very undesirable.     

Annulation of primary amines to piperazines and diazaspirocycles utilizing alpha-methyl benzyl resin

The microwave-assisted solid-phase synthesis of piperazines, 3,9-diazaspiro[5.5]undecanes and 2,9-diazaspiro[5.5]undecanes is reported. The synthesis relies on the direct annulation of primary amines with resin-bound bismesylates. Critical to the success of this chemistry was the development of alpha-methyl benzyl carbamate resin linker. This resin permits the cleavage of the heterocycles under mildly acidic conditions, free of contaminating linker-derived N-alkylated byproducts.     

The calculation of pH

A model for the pH of a mixture of a monoprotic acid and its associated salt leads to a cubic equation. This equation is shown to have real roots — one positive and two negative. The exact theory for cubic equations provides a simple expression for the positive root. Due to rounding errors the use of this formula can give poor results, so the use of Newton‐Raphson is considered.     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

Structural and stereochemical studies on marine norterpene cyclic peroxides

Isolation of a new norditerpene cyclic peroxide (12) and three new norsesterterpene cyclic peroxides (1, 2, 26) has permitted a detailed study of the stereostructures of this unusual class of marine natural product. A procedure for assigning relative and absolute stereochemistry about the peroxy moiety is outlined. An absolute stereostructure for muqubilin (11) and a revision of the previously assigned absolute stereochemistry of the sigmosceptrellins (5–10) is proposed, the latter based on the Horeau procedure.