1,5-HYDROGEN SHIFT AND OTHER ISOMERIZATION-REACTIONS OF CERTAIN ETHYLOCTADECATRIENOATES

Four new octadecatrienoic acid ethyl esters (4 - 7) were synthesized. On healing these undergo cyclization, via an intramolecular Diels-Alde r (IMDA) reaction, mainly to stereoisomers of ethyl -pentyl-1,2,3,3a,4 ,5,7a-hexahydroindenyl)butanoate (CP-1, CP-2, CP-3, CP-4 and CP-5) and yl-1,2,3,4,4a,5,6,8a-octahydronaphthyl)propanoate. 1,5-Sigmatropic hy drogen shift reactions of the trienoic esters 4-7. all possessing a co njugated Z,E structure, precede the IMDA reactions. The 1,5-hydrogen s hift reaction occurs in Z,E dienoic structures at a lower temperature than the Z.E to E,E isomerization. (C) 1997 Elsevier Science Ltd.