Synthetic studies on tricyclospirodienones; model chemistry for novel mimics of steroid substrates

Abstract

As part of a programme to synthesize aryltricyclospirodienones 3. potential steroid anti metabolites, the formation of tricyclospirodienones 4 from substituted tetralins has been studied. 1-Allyl- and 1 -(but-3-enyl)-tetralins 9 and 11 were synthesized from the 6-alkoxytetralols 8 and the corresponding pivaloates 10 using allytrimethylsilane/zinc iodide and 1-(but-3-enyl)magnesium bromide respectively, and were used to prepare the epoxides 20 and 21, the iodides 13,16 and 19, and the nitro compounds 14 and 17. Phenol-exo-spirocyclisations of the iodides were shown to proceed smoothly in the 5- and 6-exo-tetsenses; in contrast, the epoxides failed to cyclise in these formally allowed modes and only the 7-endo type, i.e. 21 (α-H)→30 was viable. Cyclisation via phenylthiiranium and phenylselenonium ions followed a similar pattern. Under acid catalysis the epoxide 21 formed the 5-exo products 36 and 37, which on further acid treatment gave the tetracycles 38 and 39 respectively. The α-oxocarbocation from the diazo ketones 41 provided the spirodienone 43. The ω-nitropropyl and ω-nitrobutyl-6-hydroxytetralins 14c and 17c underwent stereospecific intramolecular coupling between phenolate and nitronate functions to afford tricyclospirodienones 46 and 47 respectively.