STEREOCHEMICAL ASSIGMENT BY MASS SPECTROMETRY. DOUBLE BOND GEOMETRICAL ISOMERS OF 3,5-DIALKYLCYCLOHEXYLIDENE ACETIC ACID ESTERS AND 3-ALKYL-2-ALKENOATES

Article abstract of DOI:10.1016/S0040-4020(01)96456-7

Mass spectrometry is best physical method for the configurational assignment of E- and Z-3,5-dialkylcyclohexylidene acetic acid esters 1 and E- and Z-3-alkyl-2-alkenoates 2.The homoallylic cleavage resulting in the loss of the C-3 and C-5 alkyl groups from 1 and of the two δ-alkyls from 2 is a stereospecific process: the loss of the group which is adjacent to the carbonyl is significantly preferred.The stereospecifity of this fragmentation is interpreted in terms of a hidden hydrogen transfer preceding the carbon-carbon bond cleavage.