Preparation of esters containing an β-CF3 group

Malonates may be converted to esters containing an δ-CF3 group in a two-step process involving bromodifluoromethylation of the malonates followed by decarboxyalkylation-fluorination with fluoride ion in DMSO.     

Difference in thermal behaviour between 1- and 2-alkyl-5-(methoxycarbonyldiazomethyl)tetrazoles

In continuation of previous work, isomeric diazoester-substituted alkyltetrazoles 5 and 6 have been synthesized by the diazo-transfer method and studied in thermolysis reactions. Whereas the N-1 alkyl derivatives 5 give norcaradienes 7 in benzene solution and imidazotetrazoles 12 in acetonitrile, the more thermostable N-2 alkyl isomers 6 yield fluxional norcaradiene-cycloheptatriene systems, 10 – 11 , and ox-azoles 13.     

CAROTENOID PIGMENTS AND THE IN VIVO SPECTRUM OF BACTERIOCHLOROPHYLL

Abstract— The isolation of a mutant, strain PM-9, of Rhodopseudonionus spheroides with an abnormal complement of carotenoid pigments is described.
PM-9 accumulates phytoene, phytofluene, ζ-carotene and neurosporene. Semi-aerobic cultures form more ζ-carotene and neurosporene relative to total carotenoids than do photo-synthetic cultures.
PM-9 is killed on exposure to light and oxygen.
By making use of the effect of oxygen on the nature of the carotenoids in PM-9, we have shown that these pigments do not directly influence the in vivo spectrum of bacteriochlorophyll.
Diphenylamine inhibits the synthesis of coloured carotenoids in Rhodopseudonionos gelatinosa but does not change the bacteriochlorophyll spectrum.     

pH-dependent intracellular quenching of the indicator carboxy-SNARF-1

Carboxy-SNARF-1 is an emission-changing, pH-sensitive probe for measurements of intracellular pH. However, the protonated and deprotonated forms of the dye interact differently with intracellular constituents, and this imposes new requirements on the calibration of the system. Whole spectra of intracellular and extracellular C.SNARF-1 were analyzed and showed (1) intracellular quenching which was significantly greater for the deprotonated form of the dye than for the protonated state and (2) a detectable change in pK _a. Importantly for avoiding damage to cells, this mathematical analysis allowed reference spectra for fully protonated and fully deprotonated dye to be obtained without a need for spectra measured at extreme values of pH. It is not known what constituent(s) of the intracellular milieu might be responsible for the changes in dye behavior in the cell. To address this question, preliminary experiments with cell-free buffers compared the pattern seen inside the cell with quenching by a protein (bovine serum albumin; BSA) or that due to ethanol. The BSA result was completely unlike the intracellular case in that the protonated form of the dye was quenched. Buffer containing ethanol, on the other hand, was able to mimic the essential features of the intracellular spectra.     

The liquid-crystalline properties of selected cellulose derivatives

The liquid-crystalline properties of three cellulose esters, phenylacetoxy cellulose (PAC), 4-methoxyphenylacetoxy cellulose (4MPAC), and p-tolylacetoxy cellulose (TAC) and two cellulose silyl ethers, trimethyl silyl cellulose (TMSC) and t-butyldimethylsilyl cellulose (TBDMSC), are reported. Hot-stage polarized light microscopy provided evidence regarding the formation of thermotropic mesophases in the PAC, 4MPAC, TAC, and TMSC in bulk form upon heating. The concomitant DSC data showed further evidence of the thermotropic nature of these materials. PAC, 4MPAC, TAC, and TMSC formed lyotropic mesophases at 44, 48, 50, and 27 wt%, respectively in CH₂Cl₂. The presence of fingerprint patterns in wholly anisotropic solutions in conjunction with optical rotation measurements confirmed the cholesteric nature of these liquid crystalline solutions. TBDMSC formed neither a lyotropic nor a thermotropic liquid-crystalline phase due to the low degree of substitution (DS 0.68) of this derivative. The hydroxyl substituents of PAC, 4MPAC, TAC, and TMSC may be readily removed under mild conditions to regenerate cellulose.     

Rearrangement thermique des adduits du tetracyanoethylene de 2H-pyrannes

The addition of tetracyanotehylene to 2H-pyrans 1 results in a mixture of two isomeric adducts 6. The thermal decomposition of the compounds 6 gives rise to both a small percentage of the retro Diels-Alder, and a new mode of evolution leading to a mixture of furans (E+Z) 7. A detailed interpretation of the ¹³C spectra of the compounds 7 was established by comparison with the ¹³C spectra of 2,5-diphenylfuran and trans-stilbene. The structure 7 is confirmed by chemical degradation.     

Zirconium-mediated SN2' substitution of allylic ethers: regio- and stereospecific formation of protected allylic amines

A new zirconium-mediated, regio- and stereospecific SN2' substitution of allylic ethers with a nitrogen nucleophile has been developed. Cbz-protected amine products were isolated in high yield from reactions with a wide range of Z allylic ethers. A mechanism of the allylic substitution consistent with the results of the kinetics and kinetic isotope effect studies was proposed.