Tricyclic compounds

A compound of the formula ##STR81## wherein a) R.sub.1 and R.sub.2 are alkyl of 1 to 6 carbon atoms and R.sub.3 is hydrogen or A--SO.sub.2 -- or b) R.sub.2 and R.sub.3 are hydrogen and R.sub.1 is A--SO.sub.2 -- or c) R.sub.1, R.sub.2 and R.sub.3 are all hydrogen or all alkyl of 1 to 6 carbon atoms or d) R.sub.1 is A--SO.sub.2 -- or hydrogen and R.sub.2 and R.sub.3 together with the oxygens to which they are attached form --O--X--O--, X is selected from the group consisting of B(OR.sub.4)--, C(O)-- and --CR.sub.5 R.sub.6 --, R.sub.4 is hydrogen or alkyl of 1 to 6 carbon atoms, R.sub.5 and R.sub.6 are individually selected from the group consisting of hydrogen, alkyl of 1 to 6 carbon atoms and phenyl optionally substituted with 1 to 3 members of the group consisting of --OH and alkyl and alkoxy of 1 to 6 carbon atoms or R.sub.5 and R.sub.6 together with the carbon atom to which they are attached form a carbocyclic of 5 to 6 carbon atoms or e) R.sub.3 is A--SO.sub.2 -- and R.sub.1 and R.sub.2 together with the oxygens to which they are attached form --O--X--O-- or f) R.sub.1 is hydrogen and R.sub.2 and R.sub.3 are both alkyl of 1 to 6 carbon atoms or together with the oxygens to which they are attached form --O--X--O-- and A is selected from the group consisting of alkyl of 1 to 6 carbon atoms, phenyl optionally substituted with 1 to 3 alkyls of 1 to 6 carbon atoms and naphthyl optionally substituted with 1 to 5 alkyls of 1 to 6 carbon atoms.