Abstract
The first part of this thesis describes the asymmetric total synthesis of naturally occurring sesquiterpene (+)-ricciocarpin A (1) in its native optical form. Starting with 4,4-dimethyl-2-cyclohexenone (53) and following precedented procedures alcohol (+)-52 was obtained. Under Johnson’s condition, optically active ester (-)-54 was arrived at via a Claisen rearrangement of (+)-52. Not only did this rearrangement process allowed for a complete retention of stereochemical integrity, but also established the ring junction stereochemistry found in the target molecule. To facilitate the installationof the 3-furyl moiety, ester (-)-54 was transformed to aldehyde (-)-60 followed by a 1,2-addition of 3-furyllithium across the aldehydic carbonyl. In this way, an epimeric mixture of alcohols (-)-59 and (-)-62 was obtained in a relative ratio of 1:2. The undesired epimer was converted to the desired (-)-59 via a Mitsunobu reaction and which was exposed to Pd(0) and carbon monoxide to furnish□δ-lactone (+)-41. Finally, the α,β-unsaturated enone system was reduced to yield (+)-ricciocarpin A (1). The second part of this thesis details the investigation towards the asymmetric total synthesis of (-)-pisiferin (68) and (-)-isopisiferin (70) in their natural optical form. Starting from optically pure aldehyde (-)-60 and treating with the organometallic reagent resulting from metal -halogen exchange of bromide 115, an epimeric mixture of alcohol 118 was obtained in a ratio of 1:2.2. This was subsequently dehydrated to furnish compound (-)-114, the exocyclic olefin of which was selectively saturated via hydrogenation over palladium catalyst to yield ester (-)-121. Upon hydrolysis of the ester moiety of (-)-121, the resulting carboxylic acid (-)-113 was treated with trifluoroacetic acid and trifluoroacetic anhydride to achieve the desired Friedel-Crafts type cyclization process to yield tricyclic ketone (-)-112 bearing the skeletal core of the targeted natural products containing the correct stereochemistry in the ring junction. Towards natural product 70, ketone (-)-112 was reduced to ether 127, the less substituted olefin of which was selectively saturated to yield ether (-)-88. All that remains is to unveil the phenol functionality to arrive at naturally occurring (-)-isopisiferin (70).