Synthesis of steroidal derivatives containing substituted, fused and spiro pyrazolines

Microwave-Assisted Stereoselective Heterocyclization to Novel Ring d-fused Arylpyrazolines in the Estrone Series

“…On the basis of relevant references about similar reactions in the androstane series [18,37], a highly diastereoselective ring-closure was expected to occur in this case, leading to a single isomer of 5 despite the formation of two new chiral centers on C-16 and C-5′, with simultaneous acetylation of the heteroring-N(1′) by the solvent. Contrarily, the 1 H-NMR spectrum of the crude product indicated that a mixture of two acetylated pyrazoline diastereomers was obtained in a ratio of 2:1 under both MW-irradiation at 120 °C for 20 min and conventional heating for 4 h. These findings are in direct contradiction to those by Amr et al [18] and Romero-López et al [37], who independently stated that only one of the four possible pyrazoline isomers of 5 was formed in a ca. 70% yield.…”

Efficient construction of the hexacyclic ring core of palau'amine: the pKaconcept for proceeding with unfavorable equilibrium reactions

“… 10 The acylation of the secondary alcohol of 14 induced the E1cB elimination to give the desired enone 8 as a single stereoisomer. Next, treatment of 8 with hydrazine at 100 °C produced the pyrazolidine ring by 1,4-addition and hydrazone-forming reactions, 12 and because the resulting ring was not sufficiently stable for isolation and purification, benzyloxycarbonylthioisocyanate (CbzNCS) was directly added to introduce the thiourea, yielding 15 as an inseparable diastereomeric mixture. 3 e ,10 Treatment of the crude 15 with an excess amount of TFA and NaCN initiated the Strecker reaction of the desired diastereomer that possesses an α-aminomethyl side chain to give nitrile 16 , 13 while the undesired diastereomer did not give the corresponding nitrile due to the steric repulsion of the β-side chain on the concave face.…”

Synthesis and Evaluation of Pyrimidine Steroids as Antiproliferative Agents

“…The synthesis of the non-fused pyrimidine steroids ( 3a – c ) was started from commercially available pregnenolone acetate ( 1 ). The acetate group was hydrolyzed under standard basic conditions and in situ the ketone was converted into the desired α,β-unsaturated ketone 2 through a Claisen–Schmidt condensation with benzaldehyde under basic conditions [15].…”

“…To a solution of 1 (0.35 g, 1 mmol) in EtOH (5 mL) was added benzaldehyde (0.1 mL, 1 mmol) and KOH (10 mL, 10% in EtOH). The mixture was stirred at room temperature until the formation of the α,β-unsaturated ketone [15]. Then, the reaction mixture was extracted with CH 2 CI 2 (3 × 25 mL).…”