the terms lower alkoxy lower alkylthio lower alkylsulfonyl lower alkylamino lower alkylcarbonyl etc designate such groups in which the alkyl group is lower alkyl as defined above similarly lower alkenyl and alkynyl respectively designate such groups having from two to six carbon atoms inclusive preferred groups are those having up to four carbon atoms the term aryl refers to a mono or bicyclic carbocyclic or heterocyclic aromatic group such as phenyl indolyl thienyl pyrimidyl oxazolyl isoxazolyl thiazolyl isothiazolyl imidazolyl benzofuranyl benzothienyl pyridyl naphthyl and furanyl in particular phenyl pyrimidyl indolyl and thienyl as used herein the term acyl refers to a formyl lower alk en yn ylcarbonyl arylcarbonyl aryl lower alk en yn ylcarbonyl cycloalkylcarbonyl or cycloalkyl lower alk en yn ylcarbonyl group the term thioacyl is the corresponding acyl group in which the carbonyl group is replaced with a thiocarbonyl group the expression alk en yn yl means that the group may be an alkyl alkenyl or alkynyl group in formula i x is preferably ch or s and y is preferably ch 2 and most preferably they are both ch 2 r 1 is preferably acyl lower alkyl lower alkoxy a group r 10 r 11 nco u2014 or r 10 r 11 ncs u2014 wherein r 10 is hydrogen lower alkyl cycloalkyl cycloalkyl lower alkyl or aryl and r 11 is hydrogen or lower alkyl or r 10 and r 11 together with the n atom to which they are linked form a pyrrolidinyl piperidinyl or perhydroazepin group most preferably r 1 is formyl acetyl methylaminocarbonyl methylaminothiocarbonyl dimethylaminocarbonyl dimethylaminothiocarbonyl methylsulfonyl aminocarbonyl cyclopropylcarbonyl methyl pyrrolidinylcarbonyl or 4 fluorophenylaminocarbonyl r 2 is preferably hydrogen or lower alkyl most preferably hydrogen or methyl or r 1 and r 2 are linked.