A process for the preparation of a compound of formula, as a single stereoisomer or a mixture thereof, or a salt thereof wherein each of X and Y, being the same or different, is an optionally substituted C 1 -C 12 alkyl group; an optionally substituted C 3 -C 12 cycloalkyl group; an optionally substituted aryl group; an optionally substituted C 1 -C 12 alkoxy group; a halogen; hydroxy; cyano; nitro; an amine group -NR'R" or an amide group -NR'COR", wherein each of R' and R", which are the same or different, is hydrogen, an optionally substituted C 1 -C 12 alkyl group, an optionally substituted C 3 -C 12 cycloalkyl group, an optionally substituted aryl group, or R' and R", taken together, complete a heterocyclic C 2 -C 7 ring; R is an optionally substituted C 1 -C 12 alkyl group; an optionally substituted C 3 -C 12 cycloalkyl group; an optionally substituted aryl group; cyano; a COOR' group, wherein R' is as defined above; a -CONR'R" group, wherein each of R' and R", which are the same or different, is as defined above; comprising the cycloaddition reaction between a compound of formula and a compound of formula, wherein R 1 is a silyl group of formula (R 2) 3 Si-, wherein each R 2, which are the same or different, is selected from the group comprising optionally substituted C 1 -C 12 alkyl, optionally substituted C 3 -C 12 cycloalkyl, optionally substituted C 1 -C 12 alkoxy and optionally substituted aryl; or a sulphonyl group R 3 SO 2 -, wherein R 3 is an optionally substituted C 1 -C 12 alkyl group, an optionally substituted C 3 -C 12 cycloalkyl group, an optionally substituted aryl group, an optionally substituted aryl-C 1 -C 12 alkyl group; or an R 3 CO- acyl group wherein R 3 is as defined above; Z is halogen or a sulphonyl group of formula R 3 SO 2 -O-,wherein R 3 is as defined above; and R, X and Y are as first defined and, if desired, the conversion of a compound of formula to another compound of formula, and/or the resolution of a mixture of its stereoisomers into a single stereoisomer, and/or the conversion of a compound of formula to a salt thereof, and/or the conversion of a salt of a compound of formula to an unsalified compound of formula. wherein each of X and Y, being the same or different, is an optionally substituted C 1 -C 12 alkyl group; an optionally substituted C 3 -C 12 cycloalkyl group; an optionally substituted aryl group; an optionally substituted C 1 -C 12 alkoxy group; a halogen; hydroxy; cyano; nitro; an amine group -NR'R" or an amide group -NR'COR", wherein each of R' and R", which are the same or different, is hydrogen, an optionally substituted C 1 -C 12 alkyl group, an optionally substituted C 3 -C 12 cycloalkyl group, an optionally substituted aryl group, or R' and R", taken together, complete a heterocyclic C 2 -C 7 ring; R is an optionally substituted C 1 -C 12 alkyl group; an optionally substituted C 3 -C 12 cycloalkyl group; an optionally substituted aryl group; cyano; a COOR' group, wherein R' is as defined above; a -CONR'R" group, wherein each of R' and R", which are the same or different, is as defined above; wherein R 1 is a silyl group of formula (R 2) 3 Si-, wherein each R 2, which are the same or different, is selected from the group comprising optionally substituted C 1 -C 12 alkyl, optionally substituted C 3 -C 12 cycloalkyl, optionally substituted C 1 -C 12 alkoxy and optionally substituted aryl; or a sulphonyl group R 3 SO 2 -, wherein R 3 is an optionally substituted C 1 -C 12 alkyl group, an optionally substituted C 3 -C 12 cycloalkyl group, an optionally substituted aryl group, an optionally substituted aryl-C 1 -C 12 alkyl group; or an R 3 CO- acyl group wherein R 3 is as defined above; Z is halogen or a sulphonyl group of formula R 3 SO 2 -O-,wherein R 3 is as defined above; and R, X and Y are as first defined and, if desired, the conversion of a compound of formula to another compound of formula, and/or the resolution of a mixture of its stereoisomers into a single stereoisomer, and/or the conversion of a compound of formula to a salt thereof, and/or the conversion of a salt of a compound of formula to an unsalified compound of formula.