Ring transform packages

All the ring transform packages in LHASA employ binary search techniques. This means that all structural questions are to be answered with a yes or a no. Preparation of the sequence of questions relating to straightforward chemical situations poses no real problems. It is the identification and resolution of the extraordinary cases that are difficult. For example, in a Robinson disconnection for the sequence below, the geminal dimethyl substitution is a formidable problem. 

It is up to the chemist designing the tables to first perceive that this situation might occur. Second, decide whether he wishes to have the tables salvage the difficult situation and if he does, he has to manually determine what kind of chemistry should be attempted. 

The above example is a clear black or white situation. Unless the dimethyl substituent is removed, the transform just cannot proceed. The grey areas cause just as much of a dilemma for the chemist, In Marshall s synthesis of isonootkatone two possible stereoisomers could have resulted. 

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

As we have been adding to the data base at Du Pont (to the one and two group tables), the question has often been raised how much detail should we go into in the qualifiers This is somewhat of a dilemma, many of the industrial reactions we are dealing with have only been considered for a limited number of substrates. It is not clear whether qualifiers should be incorporated that restrict the transforms to only those cases where it is known to work or whether only those which are known to fail should be specifically excluded. Both ways take an immense amount of literature work to do consistently. 

---