Di-t-butyl dicarbonate and one of its dithiol analogs, practical methods of preparation for which are given, react with amino-acid esters to form the N-t-butoxycarbonyl (t-BOC) derivatives and the thiol analogs in good yield under mild conditions. The thiol analogs are stable to acidic conditions, which rapidly remove the t-BOC group itself. t-Butyl trimethylsilyl carbonate forms a (CHa)aSi ether from a M-thiol-t-BOC serine methyl ester. The N-thiol-t-BOC group can be removed from the -NHCOSR (R = t-butyl) by heating with peroxide-acetic acid. Action of the dicarbonates described above has not been attended by racemization in the cases examined. The two dicarbonates may be useful as agents for selective blocking and deblocking of amino or other groups.Recent studies (1, 2) in this laboratory have made the tricarbonates 1 and 2 readily available. From them, without isolation of the tricarbonates if desired, the corresponding dicarbonates 3 and 4 are readily prepared by treatment with tertiary amines or by mild heating (3). 1,X= 0 3,X 0 2,X =S 4,X= S R = t-butyl The ready availability of the sulfur and oxygen dicarbonates (for nomenclature, see ref. 2.) suggested that their behavior with a-amino acids should be studied, because the expected reaction (4, 5) would lead to the t-butoxycarbonyl (t-BOC) derivatives, or their sulfur analogs (thiol-t-BOC); the t-BOC group is a standard protecting group for the amino group in peptide syntheses. The reaction of 3 and 4 should allow synthesis of such derivatives under mild conditions, and might have useful applications in selective alteration of enzymes or proteins.The expected reaction (4, 5) took place readily; the aminoacid ester hydrochloride was usually used, neutralized with bicarbonate, and heated briefly in tetrahydrofuran (THF) or chloroform to give the product in good yield. Free glycine was also used successfully.
Tingle compounds are a class of alkenamides with organoleptic properties that include a numbing or a pins and needles effect that is generally perceived on the lips and in the mouth when consumed. They occur in nature in a number of botanical species. Spilanthol and Pellitorine are important examples of tingle compounds. A number of homologs and analogs were synthesized to study the effect of chain length, double bond location, and amide moiety on the tingle effect. This also provided the opportunity to study the behavior of these compounds in the collision cell of a triple quadrupole mass spectrometer. The doubly allylic 2E,6Z-alkenamides, which made up the largest class studied, fragmented in a characteristic way to produce a distonic radical cation and a cyclopropene cation. Mechanisms for the formation of these ions are proposed. The mechanisms are supported by energy-resolved mass spectrometric data, the analysis of deuterated analogs and homologs that are not doubly allylic, and exact mass measurements. Exceptions to the proposed mechanisms are also presented. These data represent the first attempt to apply mechanistic principles to the product ions observed in the MS/MS spectra of these compounds. The authors believe the results of this study will facilitate the identification of these and similar compounds and contribute to the fundamental understanding of the behavior of alkenamides in the collision cell of a triple quadrupole mass
The thermal isomerization of 3,3-dimethylcyclobutene and 1,3,3-trimethylcyclobutene have been investigated in the gas phase in the temperature ranges 150-200°C and 172-213°C respectively. These isomerizations were homogeneous first-order reactions with rate constants independent of pressure over a wide pressure range. The rate constant for the isomerization of 3,3-dimethylcyclobutene fitted the Arrhenius equation, k = 10 13.93 exp (-36,09O/RT) sec-1.Those for the 1,3,3-trimethylcyclobutene fitted the Arrhenius equation, k = 10 13-90 exp (-37,03O/RT) sec-1.The effect of alkyl substitutents on the free energy of activation for the isomerization of cyclobutenes is discussed.This paper reports a continuation of work on the kinetics of the thermal isomerization of cyclobutenes.1-4 It proposes a connection between the rates of isomerization and the position of alkyl substituents in the cyclobutene ring.
EXPERIMENTAL PREPARATION O F MATERIALS~,~-DIMETHYLCYCLOBUTENE. 3,3-Dimethylcyclopropane nitrife was prepared from 2,2-dimethylpropane-1,3-dioI by the method of Nelson et aZ. 5 The nitrile was reduced to the corresponding aldehyde using triethoxy lithium aluminium hydride.6 The 3,3-dimethylcyclopropane carboxaldehyde was converted into its toluene sulphonylhydrazone by treatment with toluenesuplhonylhydrazide and the hydrazone was decomposed in diglyme in the presence of excess sodium methoxide at 140°C. The resulting mixture of hydrocarbon products was
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