Studies in organic mass spectrometry. XIX The fragmentation of the trimethylsilyl derivatives of some 2,3‐dialkyl‐1,4‐cyclopentanediols

Abstract

The mass spectra of the TMS-ethers of the isomeric 2,3-dialkyl-1,4-cyclopentanediols are discussed. These compounds exhibit fragmentations, characteristic for the TMS-1,3-cyclopentanediol-system.The dimethyl substituted compounds display differences in the ion abundances for a number of ions, depending upon the stereochemistry of the trimethylsiloxy groups, while for longer alkyl groups only differences in the intensity of a rearrangement ion at m/e 141 are found. A considerable change in the mass spectral behaviour is found for the compounds with an 1',2'-unsaturated alkyl substituent.The observation of differences in the abundances of certain ions in the mass spectra of stereoisomers has already been used for configurational assignment of the parent compounds . This paper describes the mass spectral behaviour of the TMS-ethers of the six isomeric 2,3-dimethyl-l,4-cyclopentanediols.Characteristic fragmentations and relevant differences in the abundances of ions have been studied by deuterium labelling, experiments at low electron energy and high resolution measurements. Some of the fragmentation processes are of considerable diagnostic value for relative configurational assignments. This has also been confirmed by the study of TMS-ethers of some homologues with longer alkyl chains.An alkenyl (1',2')-substituent (R3) causes a change in fragmentation behaviour allowing differentiation between saturated and unsaturated side chains.The isomeric 2,3-dimethyl-1,4-cyclopentanediols were synthesised in our laboratory in order to obtain simple model compounds for study of more complex analogues2 : the prostaglandins from the F-serie and other 2,3-dialkyl-l , 4-cyclopentanedibls, which occur as intermediates during the total synthesis of the Fprostaglandins and result from a solved metal reduction in liquid ammonia of the corresponding 2, 3-dialkyl-4-hydroxy-2-cyclopentene-1-ones3 ' 4 .As this reaction can yield several stereoisomers, methods are required to elu-1

Quantum chemical mass spectrometry:ab initioprediction of electron ionization mass spectra and identification of new fragmentation pathways

“…Only 1,4‐rearrangements with hydrogen atoms are considered. Non‐hydrogen rearrangements are not taken into account …”