Study of the reactione + e −→K + K − in the energy range1350 \leqq \sqrt s \leqq 2400 MeV

Thee ⁺ e ^?→K ⁺ K ^? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ^± form factor |F _F ^±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment.     

Expanding the scope of the asymmetric anti-aldol addition of chiral N-amino cyclic carbamate hydrazones

An asymmetric anti-aldol addition process of ketone-derived donors that is not limited by the structure of the ketone is described. This is achieved by merging the enantioselective α,α-bisalkylation of N-amino cyclic carbamate (ACC) hydrazones with the asymmetric anti-aldol addition of ACC hydrazones. The products of this process are obtained with essentially perfect stereoselectivity. Using this procedure it is possible to gain access to ketone-based anti-aldol addition products that are inaccessible in a controlled sense via direct aldol methods.     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Non-planar smoulder propagation governed by diffusion

The steady propagation of a thin smouldering front in a half-spacehas been considered. A suitable coordinate transformation hasallowed the region near the leading edge of the front to beexamined for both a maintained planar surface and with surfacecollapse due to material shrinkage. The change in the oxidizerconcentration for a small increment in the propagation speedfor large time and surface collapse has been determined. Theinfluence of two types of nonlinear diffusion on the shape ofthe smouldering front has been found; other cases can be dealtwith in a similar manner.     

Derivatized amino acids relevant to native peptide synthesis by chemical ligation and acyl transfer

Three amino acids were converted into the derivatives 5.2 (from glycine), 6.4a and 6.4b (from alanine), and 8.3a and 8.3b (from O-benzyl serine). These N-alkylated amino acids, which can be deprotected after conversion of the carboxyl into an amide, correspond to the general structure 2.1, a compound class of use in the study of peptide segment coupling by the ligation-acyl transfer method.     

A facile and efficient direct aldol addition of simple thioesters

[reaction: see text] Simple thioesters undergo direct aldol addition to aldehydes in the presence of MgBr(2).OEt(2) and i-Pr(2)NEt using untreated, reagent-grade CH(2)Cl(2) under atmospheric conditions. The reactions proceed extremely rapidly and in excellent yield.     

Regioselective asymmetric α,α-bisalkylation of ketones via complex-induced syn-deprotonation of chiral N-amino cyclic carbamate hydrazones

The first general method for the asymmetric α,α-bisalkylation of ketones having both α- and α'-protons is described. Both excellent regio- and stereoselectivity result. The transformation is enabled by complex-induced syn-deprotonation (CIS-D), which completely reverses the inherent preference of lithium diisopropylamide (LDA) to remove the less sterically hindered of two similarly acidic protons. CIS-D also overrides the normal tendency of LDA to remove the more strongly acidic proton in a substrate having protons differing significantly in their acidity. The regiochemical outcome is, thus, the opposite of that normally obtained for kinetic LDA-mediated deprotonation of ketones and (S)-1-amino-2-methoxymethylpyrrolidine/(R)-1-amino-2-methoxymethylpyrrolidine (SAMP/RAMP)hydrazones. Conveniently, this strategy allows access to either ketone enantiomer using a single enantiomer of the auxiliary. The utility of this method is demonstrated by a concise and highly efficient formal synthesis of both (R)- and (S)-stigmolone.     

Direct carbon-carbon bond formation via chemoselective soft enolization of thioesters: a remarkably simple and versatile crossed-Claisen reaction applied to the synthesis of LY294002

Thioesters undergo chemoselective soft enolization and acylation by N-acylbenzotriazoles on treatment with MgBr2 x OEt2 and i-Pr2NEt to give beta-keto thioesters. Prior enolate formation is not required, and the reaction is conducted using untreated CH2Cl2 open to the air. The coupled products are stable synthetic equivalents of beta-keto acids and can be converted directly into beta-keto esters, beta-keto amides, and beta-diketones under mild conditions. The utility of this carbon-carbon bond-forming method is shown through the synthesis of the PI3-K inhibitor LY294002.