A new intramolecular aldol based route to benzannelated bicyclo[3.3.1]nonane derivatives

A synthetic route to the title compounds is described based on the addition of 2-Iithiobenzaldehyde ethylene ketal to cyclohexane-1,4-dione ethylene ketal followed by acid-catalysed deprotection and in situ intramolecular stereospecific aldol cyclisation, which gives 8-hydroxy-1-methoxytricyclo[7.3.1.02,7]trideca-2,4,6-trien-10-one (1a); the synthetic potential of the methodology for preparation of various derivatives is described.