{HEAD ~ The compounds} have the formula: ##STR1## wherein: {TAIL ~ the dashed line} indicates either the 4,5 unsaturated or the 4,5 dihydrofuranone ring 
{ HEAD ~ The compounds } have the formula : # # STR1 # # wherein : { TAIL ~ the dashed line } indicates either the 4,5 unsaturated or the 4,5 dihydrofuranone ring
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH