Highly stereoselective hydrogenation of 3-oxo-4-ene and -1,4-diene steroids to 5.beta. compounds with palladium catalyst

Total Synthesis of ent-Pregnanolone Sulfate and Its Biological Investigation at the NMDA Receptor

“…38−40 Its hydrogenation stereoselectively afforded diketone ent-40. 41 The sterically more accessible ketone function at C-3 was subsequently stereoselectively reduced by NaBH 4 /CeCl 3 in very good yield. Treatment of alcohol ent-41 with the pyridine−sulfur trioxide complex led to quantitative conversion to the target pregnanolone sulfate (ent-1), totaling 18 steps and 5.5% overall yield for the whole synthesis.…”

“…Its hydrogenation stereoselectively afforded diketone ent - 40 . The sterically more accessible ketone function at C-3 was subsequently stereoselectively reduced by NaBH 4 /CeCl 3 in very good yield.…”

Synthesis of [β-4,5-3H]-cholestan-3-one, a trail following pheromone component of the eastern tent caterpillar

“…Catalytic hydrogenation of 3-0x0-4-ene steroids using palladium catalysts is a convenient route to 5p-steroids. [3] The stereoselectivity which provides the @-configuration depends on the reaction medium and the functional groups associated with the steroid [4]. It has been Tritium NMR ( Table 1) was used to determine the purity of the radiolabled compound by determining the % d.e., and the extent of exchange of either a proton or a tritium at other positions of the molecule, For our purposes (scintillation counting), the location of the tritium substitution was not as crucial as the purity at the 5P-position.…”

Unified Total Synthesis of Five Bufadienolides

“…The C5double bond of 9 was stereoselectively hydrogenated from the opposite face of the C10-methyl group by catalysis of Pd/C in pyridine, providing the cis-fused AB ring 10 as a major diastereomer (β-H:α-H at C5 = 9.3:1). 18 The C3-ketone of 10 was stereoselectively reduced in the presence of the C17ketone by the action of the bulky reductant KBH(s-Bu) 3 . 19 The resultant C3-OH was protected as its tert-butyldimethylsilyl (TBS) ether to generate 11 after separating the diastereomers.…”

“…First, the preparation of tetracycle 8 started with functionalization of the A ring of 9 (Scheme ). The C5-double bond of 9 was stereoselectively hydrogenated from the opposite face of the C10-methyl group by catalysis of Pd/C in pyridine, providing the cis -fused AB ring 10 as a major diastereomer (β-H:α-H at C5 = 9.3:1) . The C3-ketone of 10 was stereoselectively reduced in the presence of the C17-ketone by the action of the bulky reductant KBH­( s -Bu) 3 .…”