Condensed cyclic and bridged-ring systems-14. Synthesis of some bridged propano-hydrophenanthrene, -hydrofluorene and polycyclic benzo-propellane derivatives through intramolecular c-alkylations of γ δ-unsaturated α'-diazomethyl ketones

Abstract

Stereocontrolled synthesis of the bridged hydroaromatic ketones 7 and 8 through regiospecific reductive cleavages of the cyclopropyl ketone 5, obtained by intramolecular keto-carbenoid addition of (±)-l-diazo-3- (1' -methyl-2',3',4' ,4a',9',10' -hexahydrophenanthren-4a' -yl)propan-2-one (1), are described. An alternate stereocontrolled synthesis of 8has been achieved by a regioselective α-oxocarbenoid insertion across the benzylic C-H (at C-4a) bond in the copper-catalyzed carbenoid decomposition of the α-diazomethyl ketone(12). The cyclopropyl ketone 15a, derived from the diazoketone (±)-1- diazo-3-(4'-methyl-2' ,3' ,9' ,9a'-tetrahydro-l'H-fluoren-9a'-yl)propan-2-one (2a) or the hydroxy ketone 17 produced by acid-catalyzed cleavage of 15a, on catalytic hydrogenation with palladium-on-charcoal and reduction with lithium in liquid ammonia produced exclusively the epimeric bridged ketones 19a and 20a respectively. Unlike the cyclopropyl ketone 15a, the corresponding 7- methoxy analogue 15b,on acid-catalyzed cleavage, produced a benzo propellenone 18 through an interesting rearrangement.