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Studies related to the Veratrum alkaloids : the total synthesis of C-nor-D-homo steriod analogue.

University of British Columbia

A sequence leading to the total synthesis of trans-anti-trans- and trans-syn-cis-C-nor-2-methoxy-8,11-diketo-10a-methyl-4b,5,6,6a,7,8,9,10,10a,10b,11-undecahydrochrysene (LXXXI and LXXXII,respectively) from the known compound, 2-methoxy-8-keto-10a-methyl-5,6,8,9, 10,10a,11,12-octahydrochrysene (XLIII), is described. Oxidation of trans-anti-trans-2-methoxy-8β-acetoxy-10a-methyl-4b,5,6,6as7,8,9,10,10a,10b,11,12-dodecahydrochrysene (LXV) by means of t-butyl chromate led mainly to the 12-keto derivative (LXVIII). An olefinic bond at the 11,12 position (LXXI) was introduced by mild reduction of LXVIII with sodium borohydride followed by dehydration with phosphorus pentoxide. Subsequent reaction at the olefinic linkage by osmium tetroxide provided mainly the β-diol LXXII which upon treatment with periodic acid gave trans-anti-trans-11 ,12-seco-11,12-dioxo-2-methoxy-8β-acetoxy-10a-methyl-4b,5,6,6a,7,8,9, 10,10a,10b11,12-dodecahydrochry-sene (LXXIV). Intramolecular aldol condensation of IXXIV with sodium hydroxide gave the C-nor-D-homo diol aldehyde LXXIX. Oxidation of the latter with Jones reagent followed by deformylacion of the resulting diketo aldehyde IXXX provided the isomeric diketones LXXXI and LXXXII. It is felt that these latter substances show promise as useful intermediates for the total synthesis of Veratrum alkaloids. In another sequence designed as a model for the subsequent elaboration of LXXXI and LXXXII to the Veratrum alkaloid system, trans-anti-trans-anti-2-keto-8β-hydroxy-10a-methyl -2,3,4,4a, 4b, 5,6, 6a,7, 8,9,10,10a,10b,11,12-hexadecahydrochrysene (XCII) was methylated at C-1via the pyrrolidyl dienamine XCIII. A detailed discussion of the nuclear magnetic resonance spectra of the hydrochrysene compounds is also presented.

Text

2011-08-16

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http://hdl.handle.net/2429/36687

Chemistry

University of British Columbia

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