Asymmetric Dihydroxylation Syntheses of Anthracyclinones
Abstract (Summary)Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. The methylidene tetracycle (12) has been synthesised in 11 steps from quinizarin (5) in an overall yield of 38%. The sequence uses a highly efficient selective dihydroxylation step, and is completed by an intramolecular ene cyclisation reaction. The racemic alkene (12) has been subjected to asymmetric dihydroxylations (AD) following on from related work by Rustenhoven.53 The products resulting from reaction with both AD-mix-? and AD-mix-? have been characterised, and an assignment of stereochemistry made using 1H n.m.r. in conjunction with nOesy n.m.r. and molecular modelling of acetonide derivatives. An X-ray structure obtained for the acetate (125) confirms the stereochemical assignments. Two novel total syntheses of the ethylidene compound (47) as a mixture of (E) and (Z) isomers, are presented. One includes a similar selective dihydroxylation as a key step. AD reactions have been performed on the racemic substrate and the resulting triols purified by reverse phase high performance liquid chromatography (h.p.l.c.). The stereochemistry at C7 and C9 has been assigned by analogy with the related methylidene compounds, but the Cl ' stereochemistry remains unassigned. The silyloxy alkene (13) and the 6-demethoxy alkene (14), were both synthesized using the selective dihydroxylation methodology. The sequence to the latter compound uses a tandem Claisen-demethoxylation reaction involving sodium dithionite, as a key step. AD chemistry on the silyloxy alkene (13) gave only one cis diol for each AD-mix-? and AD-mix-? reaction, and the stereochemistry was assigned as above. Reaction of the Admix reagents with the 6-demethoxy alkene (14), gave only starting material and the naphthacenedione (153).
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:01/01/1997