A. S. Campos Neves

Copper-catalysed allylic oxidation of Δ5-steroids by t-butyl hydroperoxide

Abstract Δ 5 -7-Oxosteroids are efficiently prepared from Δ 5 -steroids with t -BuOOH and a copper catalyst, either Cu(II) and Cu (I) salts or Cu metal; selectivity in the presence of a secondary alcohol is observed.

Oxidations with potassium permanganate — metal sulphates and nitrates. β-Selective epoxidation of Δ5-unsaturated steroids

Abstract The β-epoxidation of 3 β -acetoxy-Δ 5 -unsaturated steroids has been achieved with mmerous potassium permanganate-metal sulphates and nitrates with a high degree of stereoselectivity. 5β,6β-Epoxides are formed in a one step reaction in good yields and using very low cost reagents. The best results were achieved with KMnO 4 /Fe 2 (SO 4 ) 3 .nH 2 O.

A novel oxidation of homoallylic alcohols under sonochemical conditions

Abstract The oxidation of 3β-hydroxy-Δ 5 -cholestenes, -pregnenes and -androstenes to the corresponding Δ4-3,6-diones has been achieved in high yields by a new one-step process, using tetra- n -propylammonium perruthenate with 4-methylmorpholine N-oxide as co-oxidant, under sonochemical conditions.

Sonochemical reduction of α, β-epoxy ketones and α′-oxygenated analogs by aluminium amalgam

Abstract The sonochemical reductive opening of α, β-epoxy ketones and their α′-oxygenated (-OH or -OAc) analogs by aluminium amalgam allows shorter reaction times, better yields of the respective β-hydroxy ketones and minimization of by-products. The rates of these reactions are affected by the intensity of the acoustic waves and by temperature.

Ultrasound assisted zinc reactions in synthesis 1. Efficient reduction of enones

Abstract Zinc reduction of α, β-unsaturated ketones in acetic acid has been efficiently accomplished under sonochemical conditions. Different α-enone systems give two kinds of products: olefins and allylic alcohols. Regio- and stereoselective are reported.

Ultrasound assisted zinc reactions in synthesis 2. A new clemmensen-type reduction

Abstract A mild and efficient method is described for the reduction of carbonyls to methylene groups. Under ultrasonic irradiation, deoxygenation of 3-oxosteroids with zinc dust in acetic acid or acetic acid/water was achieved in 15 minutes. The observed selectivity at C-3 in the presence of 17- and 20-oxo groups is discussed.

3α,4β-Dihydroxy-5α-androstan-17-one

The crystal structure of the title compound, C 19 H 30 O 3 , is reported. This steroid was obtained as an intermediate in the synthesis of formestane. The molecules are held together by a network of hydrogen bonds involving the carbonyl and hydroxyl groups.

Ultrasound assisted oxidations and reductions in steroid synthesis

Abstract Ultrasonic irradiation made feasible some important oxidative and reductive reactions in steroid synthesis. These unusual conditions have improved existing methods and promoted new ones. The very common 5-en-3β-ol homoallylic system in steroids was oxidized to 4-ene-3,6-diones by a new one-step process, using tetra- n -propylammonium perruthenate with a co-oxidant, under sonochemical conditions. Ultrasonic irradiation has been also successfully used to promote the generation of radicals in the hypoiodite reaction, in order to prepare tetrahydrofurans as precursors of 19-hydroxy-Δ 5 -steroids. Application of ultrasound to aluminium amalgam reductive opening of α,β-epoxy-ketones improved the reaction rates and yields of β-hydroxy ketones, in particular for α′-oxygenated counterparts. Zinc reduction of α,β-unsaturated oxosteroids has been also enhanced by ultrasound. Fast quantitative reactions led to olefins or allylic alcohols, according to the α-enone system used. Regio- and stereoselectivities are marked. A new Clemmensen-type reduction promoted on the last conditions gave a mild and effcient method to reduce selectively 3-oxo groups in polihydroxysteroids.

3α-Hydroxy-5α-androstane-4,17-dione

The asymmetric unit of the title compound, C 19 H 28 O 3 , contains two independent molecules with almost identical geometry. The molecules have a planar 5a configuration as a result of a trans-A/B junction of the rings. The compound crystallizes in a triclinic cell, which is unusual for steroids. The molecules are linked head-to-tail via hydrogen bonds between the ring A hydroxyl group and the ketone group of ring D, forming two independent chains running along the c axis.

3α,4α-Epoxy-5α-androstan-17-one

The structure of the title compound, 3α,4α-epoxy-5α-androstan-17-one, C19H28O2, shows evidence of the strain caused by the presence of an epoxy O atom bonded to C3 and C4 in the molecule. Ring A has a sizeable distortion and assumes a conformation intermediate between 10-β-sofa and 1,10-half chair. Ring D has a 14-α-envelope conformation. Cohesion of the crystal is due only to van der Waals interactions and weak intermolecular C—H⋯O interactions.