Application of the Reich Iodoso syn-Elimination for the Preparation of an Intermediate Appropriate for the Synthesis of both Hexacyclic Steroidal Units of Cephalostatin 7.
Hecogenin actetate 5 was converted to an intermediate suitable for construction of both "North" and "South" hexacyclic spiroketals present in cephalostatin 7.The key chemical transformations involved are: (1) the Reich iodoso syn-elimination of iodine 18; (2) Rhodium catalyzed intermolecular oxygen alkylation of secondary neopentyl alcohol 21; and (3) Intramolecular Wadsworth-Emmons reaction to provide the ester precursor of aldehyde 4.
Oxidative fragmentation of pregna-14,16-dien-20-ones to 14 beta-hydroxyandrost-15-en-17-ones.
Two methods have been developed for efficient conversion of pregna-14,16-dien-20-ones into 14 beta-hydroxyandrost-15-en-17-ones. One procedure consists of treatment of the ring-D dienone successively with sodium borohydride and singlet oxygen. The reaction is illustrated by the conversion of pregna-14,16-dien-20-one 1 into 14 beta-hydroxyandrost-15-en-17-one 3, via the corresponding allylic alcohol 2. Although this two-step procedure is simple, it provides 3 in relatively low yield, accompanied by a smaller amount of the isomeric 14 alpha-hydroxyandrost-15-en-17-one 6. An alternative one-step conversion is achieved by treatment of dienone 1 with a peroxyacid in the presence of a strong protic acid. This process is illustrated by the two-step conversion of dienone 1 into hydroxy ketone 11 in 51% overall yield (Scheme 5) and by the analogous conversion of dienone 13 into hydroxy ketone 24 in 61% overall yield (Scheme 11).
Fell, Jennifer D,Heathcock, Clayton H
p. 4742 - 4746
(2007/10/03)
α,β-epoxy vinyl triflates in Pd-catalyzed reactions
(matrix presented) Reactions of steroidal αβ-epoxy vinyl triflates in Pd-catalyzed reactions are described. Oxidative insertion of Pd0 into the C-O bond, giving vinylpalladium 12, is faster than formation of the π-allyl derivative from the vinyl epoxide. Although 12 can be trapped under certain conditions, it eventually rearranges to palladium alkoxide 14, which is in equilibrium with 15 and/or 10.
Yamamoto, Kana,Heathcock, Clayton H.
p. 1709 - 1712
(2007/10/03)
Lead tetraacetate cleavage of 20-hydroxyspirostans.
-
Mitsuhashi,Shibata,Uehara
p. 301 - 303
(2007/10/10)
More Articles about upstream products of 5821-04-5