A process for the preparation of a compound of formula wherein a is an integer from 0 to 3; R 1 and R 2 are each independently selected from the group consisting of H, OH, protected hydroxyl, alkyl, alkenyl, alkynyl, acyl, aryl, heteroaryl, cycloalkyl or heterocycle; wherein the alkyl, alkenyl, alkynyl or acyl is optionally substituted with one or more substituents independently selected from the group consisting of halogen,-OH, alkyl, -O-alkyl, NR A R B, -S-alkyl, -SO-alkyl,-SO 2 -alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl or heterocycle; wherein R A and R B are each independently selected from hydrogen and C 1-4 alkyl; wherein the aryl or heteroaryl, whether alone or as part of a substituent group, is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, -COOH, -C -C 1-4 alkyl,-C O-C 1-4 alkyl, NR C R D, -S-alkyl, -SO-alkyl and -SO 2 -alkyl; wherein R C and R D are each independently selected from hydrogen and C 1-4 alkyl; R 3 is selected from the group consisting of H, alkyl, acyl, -SO 2 -alkyl, -SO 2 -aryl and -SO 2 -heteroaryl; wherein the alkyl is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, NR E R F, -S-alkyl, -SO-alkyl,-SO 2 -alkyl, aryl and heteroaryl; and wherein R E and R F are each independently selected from hydrogen and C 1-4 alkyl; wherein the aryl or heteroaryl, whether alone or as part of a substituent group, is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, NR G R H, -S-alkyl, -SO-alkyl and -SO 2 -alkyl; wherein R G and R H are each independently selected from hydrogen and C 1-4 alkyl; each ------- represents a single or double bond; provided that both-groups are not double bonds, and wherein denoted, dash marks indicate the points of attachment; or a pharmaceutically acceptable salt or ester thereof; the process comprises reacting a compound of formula, wherein each X is independently selected from the group consisting of Br, F and Cl, with a compound of formula wherein R 0 is H or OH, in the presence of a protic or first Lewis acid catalyst to form a compound of formula; then either (i) cyclizing the compound of formula by reacting the compound of formula with a second Lewis acid catalyst to form a compound of formula; and then reacting the compound of formula with a reducing agent to form the compound of formula (ii) reacting the compound of formula with a reducing agent to form a compound of formula; and then cyclizing the compound of formula by reacting the compound of formula with a second Lewis acid catalyst to form the compound of formula. a is an integer from 0 to 3; R 1 and R 2 are each independently selected from the group consisting of H, OH, protected hydroxyl, alkyl, alkenyl, alkynyl, acyl, aryl, heteroaryl, cycloalkyl or heterocycle; wherein the alkyl, alkenyl, alkynyl or acyl is optionally substituted with one or more substituents independently selected from the group consisting of halogen,-OH, alkyl, -O-alkyl, NR A R B, -S-alkyl, -SO-alkyl,-SO 2 -alkyl, alkenyl, alkynyl, aryl, heteroaryl, cycloalkyl or heterocycle; wherein R A and R B are each independently selected from hydrogen and C 1-4 alkyl; wherein the aryl or heteroaryl, whether alone or as part of a substituent group, is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, -COOH, -C -C 1-4 alkyl,-C O-C 1-4 alkyl, NR C R D, -S-alkyl, -SO-alkyl and -SO 2 -alkyl; wherein R C and R D are each independently selected from hydrogen and C 1-4 alkyl; R 3 is selected from the group consisting of H, alkyl, acyl, -SO 2 -alkyl, -SO 2 -aryl and -SO 2 -heteroaryl; wherein the alkyl is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, NR E R F, -S-alkyl, -SO-alkyl,-SO 2 -alkyl, aryl and heteroaryl; and wherein R E and R F are each independently selected from hydrogen and C 1-4 alkyl; wherein the aryl or heteroaryl, whether alone or as part of a substituent group, is optionally substituted with one or more substituents independently selected from the group consisting of halogen, -OH, alkyl, -O-alkyl, NR G R H, -S-alkyl, -SO-alkyl and -SO 2 -alkyl; wherein R G and R H are each independently selected from hydrogen and C 1-4 alkyl; each ------- represents a single or double bond; provided that both-groups are not double bonds, and wherein denoted, dash marks indicate the points of attachment; or a pharmaceutically acceptable salt or ester thereof; the process comprises reacting a compound of formula, wherein each X is independently selected from the group consisting of Br, F and Cl, with a compound of formula wherein R 0 is H or OH, in the presence of a protic or first Lewis acid catalyst to form a compound of formula; then either (i) cyclizing the compound of formula by reacting the compound of formula with a second Lewis acid catalyst to form a compound of formula; and then reacting the compound of formula with a reducing agent to form the compound of formula (ii) reacting the compound of formula with a reducing agent to form a compound of formula; and then cyclizing the compound of formula by reacting the compound of formula with a second Lewis acid catalyst to form the compound of formula.