Compounds of formula V ##STR1## and C.sub.1 -C.sub.6 carboxylic acid esters thereof, wherein R.sub.1 is selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, n-C.sub.3 H.sub.7, isoC.sub.3 H.sub.7, CH.sub.2 --O--CH.sub.3, CH.sub.2 --O--C.sub.2 H.sub.5, CH.sub.2 --O--CHF.sub.2 and cyclopropyl and R.sub.2 is cyclopropyl or C.sub.1 -C.sub.3 alkyl.