Selective reactions and modification of functional groups in steroid chemistry

Ammonium Formate/Palladium on Carbon: A Versatile System for Catalytic Hydrogen Transfer Reductions of Carbon-Carbon Double Bonds

“…The unhindered endocyclic D 2 -double bond in 5a-cholest-2-ene (15) 20 was easily reduced to 16, while the more hindered D 2 -double bond in compound 26 21 having a lanostane skeleton required 20 hours reaction time to give dihydrolanosterol (27). 22 In accord with previous data, 23 the trisubstituted D 5 -double bond in compounds 19 24 and 25 was found unreactive, as was the highly hindered D 8double bond in lanosterol (28). The The reduction of vinyl-and allyl-substituted steroids, 17 30 and 19, gave the respective saturated compounds 18 31 and 20, 32 with excellent, practically quantitative yield.…”

Traceless bond construction via rearrangement of N-Boc-N-allylhydrazones giving 1,1-disubstituted olefins

“…17,18 Both required aldehydes 10a and 10b where synthesized from ergosterol over several steps. 5,6-Dihydroergosterol (8), obtained by hydrogenation of ergosterol in almost quantitative yield, 19,20 was oxidized with chromic acid to give 5,6-dihydroergosterone (9a). 18 Regioselective ozonolysis of the side chain olefinic group gave the aldehyde 10a in good yield, subsequent condensation with N-Boc-allylhydrazine 5 gave the desired hydrazone 11a.…”

Development of a Concise Synthesis of Ouabagenin and Hydroxylated Corticosteroid Analogues

“…An overwhelming amount of literature evidence has suggested that the A ring of a steroid skeleton exhibits higher reactivity than the rest of the tetracyclic framework. 22 Thus, we posited that the A ring be fully elaborated before the rest of the molecule in the approach toward ouabagenin ( 1 ). Several scenarios exist for the elaboration of the A ring using the putative steroid intermediate 10 derived from cortisone acetate ( 9 ) following C17–C20 cleavage (Figure 2 ).…”