STARTING MATERIAL ORIENTED RETROSYNTHETIC ANALYSIS IN THE LHASA PROGRAM .3. HEURISTIC ESTIMATION OF SYNTHETIC PROXIMITY

A procedure is described for deriving a numerical representation of the synthetic proximity of two compounds, that is, the expected ease with which one could be converted to the other. The procedure has been used for the starting material oriented retrosynthetic strategy in the LHASA program. Account is taken of the number and types of atoms already mapped by another procedure,2 the number of atoms which must be changed to interconvert the compounds, and the changes which must be made to functionality, bonding, and stereochemistry. Where changes are necessary, account is taken of the proximity of facilitating functional groups.