The fatty acids present in beer and hops were found to have pronounced effects on gushing, some at concentrations of I ppm or less. Saturated fatty acids are weak gushing promoters, while unsaturated adds are powerful suppressants. A parallel structure-activity correlation also exists in a series of a-acid derivatives and their analogues. Compounds with the unsaturated side-chains intact showed either weak suppressant activity or none at all. Loss of carbon-carbon unsaturation through hydrogenation or cyclization produced powerful gushing promoters, but reduction of carbonyl unsaturation as in p-isohumulones, or loss of side chains as in humulinic acids had no effect on gushing. Promoter and suppressant effects of the compounds tested were non-specific and mixtures of unsaturated fatty acids suppressed all instances of gushing, whether natural or artificially induced. The results indicate that beer normally contains both gushing promoters and suppressants, and gushing may sometimes be due to an imbalance between them.

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2-AI kylthiazolin-5-ones resemble the 2-aryl compounds in that they are readily enolisable and can easily be acylated on oxygen. In contrast 2-alkoxythiazolin-5-ones do not enolise in polar solvents and can only be acylated with the aid of a strong base such as sodium hydride.Research Centre, Sitting bo urn e, Kent THERE are four possible structures [(I)-(IV)] for the 2,4-disubstituted thiazolin-5-ones (referred to throughout the text simply as thiazolinones). Examination of the i.r. spectra of 4-alkyl-2-phenylthiazolinones has shown that these compounds exist in a keto form [(I) or (11)] in solvents such as chloroform or in the undiluted state, but are enolised to a great extent in polar solvents such as dimethyl sulphoxide (DMSO). The salts of these compounds appear to exist in an enol form [protonated (111)], since they show an OH band in the i.r. spectrum.l The lH n.m.r. spectra of certain 4-alkyl-2-phenylthiazolinones have been examined.2 The spectrum of 4-isopropyl-2-phenylthiazolinone indicates that the two methyl groups of the isopropyl group are non-equivalent, since their signals appear as two separate doublets. As the signals do not coalesce on heating this must be due to fundamental asymmetry, not to restricted rotation.2 The structure of this compound must therefore be (I) (A2-form) rather than (11) (h3-form), since C-4 is asymmetric. The asymmetry is lost on salt formation.We have studied the n.m.r. spectra and chemical properties of 2-alkyl-and 2-alkoxy-thiazolinones in order to determine the structures of these compounds. 2,4-Dialkylthiazolinones resemble 4-alkyl-2-arylthiazolinones, but the alkoxy-compounds exhibit unexpected properties.2,4-Dialkylthiazolinones were made by cyclisation of N-thioacylamino-acids with phosphorus tribromide or dicyclohexylcarbodi-imide.4 As in the case of 2-phenylthiazolinones, treatment with acetic anhydride yields the thiazolyl a~e t a t e .~ The thiazolinones are stable, distillable liquids, provided that a 4-substituent is present.The i.r. spectra of the compounds indicate that they exist in a keto form [vmax. ca. 1730 (GO) and ca. 1635 cm-I (C=N)], and a comparison of the U.V. spectrum (cyclohexane) of 4-isobutyl-2-methylthiazolinone [ lmx. 245 nm (E 1-6 x 1071 with that of 2,4,4-trimethylthiazolinone [A,m,. 242 nm (E 1.67 x lo3)], which can only exist as structure (I), strongly supports this idea.The lH n.m.r. spectrum of 4-isopropyl-2-methylthiazolinone in CDCl, (Figure 1) confirms this view. The isopropyl methyl groups appear as a pair of doublets (6 0.82, 0.89, 1.14, and 1.21 p.p.m.) as they do in the spectrum of the 2-phenyl analogue.2 The isopropyl methine proton signal is a doublet of septets (centred at about 6 2.38 p.p.m.) and the 2-methyl signal is a doublet (6 2.44 and 2-65 p.p.m.). Addition of D20 to the CDC& solution ( Figure 2) causes almost complete disappearance of the 4-H signal, simplifies the isopropyl methine signal, and reduces the 2-methyl signal to a singlet. The 4-proton is thus shown to be readily exchangeable and also to be coupled a...

An extremely mild protocol that employs readily available starting materials, i.e., aldehyde, amine and alkyl diazoacetate, returns structurally diverse N-substituted-C-2/3-difunctionalised aziridines in excellent yields and stereoselectivities when pyridinium triflate is incorporated as an organocatalyst. The reaction process is environmentally benign affording water and nitrogen as the only by-products. This racemic protocol paves the way for the development of novel asymmetric organocatalysts capable of generating optically active aziridines