Electron impact mass spectra of 2-hydrazono-1,3-thiazolidin-4-one derivatives

Mass fragmentation of 2-hydrazono-1,3-thiazolidin-4-ones is dominated by two processes, namely cleavage of the hydrazone fragment with accompanying proton transfer from the latter to the thiazolidine ring, and cleavage of a hydrazone imide residue.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1117–1119, August, 1990.     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-dithiolanes

Electron impact induced fragmentations of the title compounds were studied by exact mass measurement and metastable ion analysis. Sulphur atoms within the ring effectively stabilize the positive charge. In most cases the loss of the larger substituent, and not the other, methyl group, gives rise to the base peak in the spectrum. Examination of competing metastable transitions shows that generally this is also the lowest activation energy primary process. In general primary ring cleavage reactions are not important unless there is a heteroatom in the substituent that can assist this cleavage.     

Electron impact induced fragmentations of some 2,2-disubstituted 1,3-oxathiolanes

The electron impact induced fragmentations of nine 2,2-disubstituted 1,3-oxathiolanes have been studied by means of exact mass measurement and metastable ion analysis. The ring cleavage almost always takes place so that the C(2)? S and C(5)? O bonds are broken, leading to the most stable products. The nature of the substituents determines the primary fragmentations of molecular ions. Ring cleavage is important only if both substituents are alkyl groups or if the carbon attaching to the ring has an alkyl character. The loss of the substituent becomes the most favourable process if it is attached to the ring through the electron-deficient carbon atom.     

Electron impact mass spectra of meliacins

The electron impact mass spectra of some new meliacins and their derivatives are discussed. The major fragmentation modes include the functional group losses, the different ring cleavages and the loss of the furan residue as neutral fragments. A mechanism for the loss of the furan moiety from the molecular ion is discussed in detail with the help of deuterium labelling, high resolution and metastable data.     

Electron impact mass spectra of 5,5-bis(carboethoxy)-1,3-dioxanes

Electron impact-induced fragmentations of 2-substituted 5,5-bis(carboethoxy)-l,3-dioxanes were studied by exact mass measurements and metastable ion analysis. The substituent R on C(2) of the heterocyclic ring has little influence on the principal cleavage reactions. Elimination of CH₂O/CO and C₂H₄O/C₂H₄/C₂H₅OH are common fragmentations for ions containing the 1,3-dioxane moiety or the OC₂H₅ group, respectively. The abundant ions at m/z 173 and 127 serve as structural probes for the class of compounds studied. Primary fragmentations implying the ester function are of little importance.     

Electron impact studies—LXVII. The mass spectra of alkyl-1,3-dithianes

The mass spectra of 1,3-dithiane, 2-methyl- and 2,2-dimethyl-1,3-dithiane have been studied by ²H labelling and metastable defocusing. The various molecular ions eliminate S₂H. to produce the ions [C₄H₇]⁺, [C₅H₉]⁺ and [C₆H₁₁]⁺ respectively, each of which scramble the hydrogens either before or accompanying further decomposition. Other processes are complex, but parallel those already reported for 2-aryl-1,3-dithianes.     

Electron impact mass spectra of some enamines

The mass spectra of α,β-diarylaminocrotonic acid anilides have been determined and the fragmentation pathways are now discussed. The proposed pathways have been confirmed by deuterium labelling, the spectrum of the model compound, or the appropriate metastables. The detailed electron impact data are given.     

Electron impact mass spectra of chlorinated methyl propanoates

The mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3-dichloropanoate (38%). In most cases α-cleavage gives the base peak [COOCH₃]⁺, and the loss of a chlorine atom from the molecular ion is characteristic of the 3-chloro, 3,3-dichloro and 3,3,3-trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH₃OH, CH₂CO, CO₂ and CO from the [M? Cl]⁺ ion. α-Cleavage and the loss of Cl^˙ gives an intense [M? COOCH₃? Cl]^+˙ peak, which is the base peak in the spectra of the 2,3-dichloro and 2,3,3-trichloro compounds.     

Electron impact mass spectra of some new macropolycycles

Mass spectra of some macropolycycles have been studied. Normal and metastable (B/E) mass spectra are presented. The fragmentation patterns and the structures of the main ions are discussed.     

Electron impact mass spectra of synthetically modified milbemycins

The potent endectocide 23-(O-methyloximino)-F28249α and related compounds were identified and characterized by mass spectrometry. The fragmentation pathway of 23-(O-methyloximino)-F28249α was identified by its high-resolution mass spectrum and the electron impact unit mass spectra of its homologs. This fragmentation pathway is presented and discussed.     

Electron impact mass spectra of substituted β-nitrostyrenes

Peaks for the M^+., [M-OH]^+., [M-HNO₂]^+. and [M-H₂NO₂]⁺ ions are characteristic in the electron impact mass spectra of trans--nitrostyrenes. The loss of NO, CONO, and CHNO radicals is accompanied by isomerization of the molecular ions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1926–1929, August, 1990.     

Substituted 1-amino-cyclopentenes from 2,3-diamino-1,3-butadienes and nitroalkenes

2,3-Diamino-1,3-butadienes (1) reacted with β-nitrostyiene or nitroethene to afford a mixture ofisomeric 1,5-diaminoo-5-methyl-4-nitro-cyclopentenes (3 and 4). The configuration of the main isomers (3) was established by X-ray diffraction analysis which also revealed the great steric crowding of this molecule. The conformation of the cyclopentene ring in 3 in the solid state is also discussed. The enamines (3 and 4) were hydrolyzed to the corresponding aminoketones (5 and 6) which, on reduction, gave the same diaminoketone (7).     

Sequential cross-coupling of 1,4-bissilylbutadienes: synthesis of unsymmetrical 1,4-disubstituted 1,3-butadienes

A mild and general and stereospecific cross-coupling reaction of unsymmetrical 1,4-bissilyl-1,3-butadienes has been accomplished. By the use of either a benzyldimethylsilyl or 2-thienyldimethylsilyl unit at one end of the dienylsilanol, a selective cross-coupling could be effected under mildly basic conditions (KOTMS) to afford 4-aryl-1,3-dienylsilanes in excellent yield for a wide range of aryl and alkenyl coupling partners. The second cross-coupling could be effected cleanly by the action of TBAF with electron-rich or electron-poor halides. The sequential process could be telescoped into a "one pot" procedure with overall excellent yields of the unsymmetrical 1,4-diaryl-1,3-butadienes.