C−H Acetoxylation‐Based Chemical Synthesis of 17 β‐Hydroxymethyl‐17 α‐methyl‐18‐norandrost‐13‐ene Steroids

Palladium‐catalyzed C?H acetoxylation has been proposed as a key transformation in the first chemical synthesis of steroids bearing a unique 17β‐hydroxymethyl‐17α‐methyl‐18‐nor‐13‐ene D ‐fragment. This C?H functionalization step was crucial for inverting the configuration at the quaternary stereocenter of a readily available synthetic intermediate. The developed approach was applied to prepare the metandienone metabolite needed as a reference substance in anti‐doping analysis to control the abuse of this androgenic anabolic steroid.     

A cyclopropanol approach to the synthesis of both enantiomers of the C13-C21 fragment of epothilones

Efficient syntheses of both enantiomers of the C13-C21 fragment of epothilone molecules have been performed by use of enantiomeric oxiranyl-substituted cyclopropylsulfonates as key intermediates. The latter were obtained by the cyclopropanation of easily available (R)-methyl 2,3-O-isopropylideneglycerate and subsequent manipulation of the functional groups. Asymmetric allylation of 1-formylcyclopropyl pivalate led to an alternative precursor of the target compounds with moderate enantioselectivity.     

Synthesis of epothilone D with the forced application of oxycyclopropane intermediates

The total synthesis of epothilone D with six-fold application in the intermediate stages of successive cyclopropanation — opening or cleavage of the three-membered ring was performed. These transformations underlie the new stereoselective method developed for coupling fragments C⁷–C¹² and C¹³–C²¹ in the target molecule.     

Palladium-catalyzed reactions of cyclopropanols bearing oxazoline directing group

Cyclopropanols bearing oxazoline directing group were investigated in palladium-catalyzed reactions. When the directing group and cyclopropanol unit were bonded through two- or three-carbon spacer, formation of unusual products was observed. Oxidative ring opening proceeded with uncommon regioselectivity providing linear enones as main products. The reaction of such cyclopropanols with aryl iodides and silver acetate furnished diarylated α-methylene ketones, which cannot be obtained from cyclopropanols lacking oxazoline ring under the same conditions.     

Total synthesis of epothilone D by sixfold ring cleavage of cyclopropanol intermediates

The ring-opening or ring fragmentation reactions of cyclopropanol intermediates are used in the total synthesis of epothilone D for the creation of trisubstituted double bonds, an ethyl ketone functionality, as well as for the protection of carboxylic and ester groups. Epothilone D is obtained in 1.6% overall yield (24 steps in the longest linear sequence) starting from (R)-methyl 2,3-O-isopropylideneglycerate. The key cyclopropanol intermediates are efficiently obtained by titanium(IV)-catalyzed reactions of readily available esters with Grignard reagents.     

A short convergent synthesis of the side chains of brassinolide,cathasterone, and cryptolide

A new approach to steroidal derivatives of the campestane series, containing the 22α-hydroxy-, 22α,23α-dihydroxy-, and 22α-hydroxy-23-ketone moieties characteristic of brassinolide and its congeners, has been developed. The key step is the coupling of a steroidal C-22 aldehyde with an anion derived from a specially synthesized thioacetal-containing chiral synthon. The cathasterone and cryptolide side chains are prepared by reductive or hydrolytic thioketal removal, respectively. The brassinolide side chain is obtained by DIBAL-H reduction of the TBS-protected 22α-hydroxy-23-ketone.