Lj. Lorenc

Configuration and reactivity of ten-membered 5,10-seco-compounds obtained by fragmentation of 5-hydroxy-steroids

Abstract Assignment of configuration to the 1,10-double bond in the cis-trans isomeric 3β-acetoxy-5,10-seco-1,10-cholesten-5-ones has been achieved by means of NMR spectrometry. Some reactions of these new compounds have been studied and, as expected from conformational analysis, it was found that only the trans-isomer readily undergoes transannular cyclizations.

Lead tetraacetate oxidation of saturated aliphatic alcohols.—III : Unbranched primary and secondary alcohols

Abstract The action of lead tetraacetate, in benzene solution, on various unbranched primary and secondary aliphatic alcohols containing 4 to 12 carbon atoms has been investigated and the ratio of carbonyl compounds, cyclic ethers and fragmentation products determined. The results obtained are discussed with regard to the number and length of the n-alkyl rests attached to the carbinol carbon atom of the starting alcohol.

A convenient synthesis of 1α- and 1β-hydroxycholesterol

Abstract An efficient procedure for the preparation of 1α-hydroxycholesterol 3-acetate 4 is described, which starts from cholesterol and involves as key steps transannular cyclization of the ten-membered ring ontaining (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one 1 to the oxetane derivative 1α,5-epoxy-5α-cholestan-3β-ol acetate 3, and opening of the four-membered ether ring in the latter compound. 1β-Hydroxycholesterol diacetate 9 was obtained by oxidation of 4 to the 1-oxo derivative 8, followed by metal hydride reduction and acetylation.

Reactions with lead tetraacetate—IV : Oxidation of saturated aliphatic alcohols—II; Alcohols of low molecular weight

Abstract The action of lead tetraacetate on ethanol, 1-propanol, 2-propanol and 2-butanol has been studied under various experimental conditions, and it was found that the tetravalent lead compound reacts with alcohols in ways not so far observed. The possible reaction schemes are discussed in terms of homolytic and heterolytic cleavage of the intermediate alkoxy lead acetate complexes.

Condensation of isatin with diketones

Abstract The condensation of isatin with enolisable acyclic and alicylcic 1:3-diketones has been investigated and the structures of the acylated cinchoninic acids obtained have been determined. The condensation of acetonylacetone with potassium isatate is also described. Condensation of isatin with 1:3- cyclo hexadiones in neutral or acid media has been shown to give products different from those in alkaline condensation.

Synthesis, structure and reactions of seco-steroids containing a medium-sized ring—IX : Reactions of Δ1(10)-unsaturated 5-oxo-5,10-seco-steroids with hydroxylamine and n-methylhydroxylamine

Abstract When treated with hydroxylamine or N-methylhydroxylamine, in the presence of proton donor catalysts, trans-Δ1(10)-unsaturated 5-oxo-5,10-seco-steroids, such as 3 (but not the corresponding diastereomeric cis-compounds), are converted stereospecifically and in good yield to isoxazolidine derivatives (e.g. 4 and 13), resulting from transannular 1,3-dipolar addition of the intermediately formed oximes and nitrones to the trans-double bond in the cyclodecene ring moiety of the seco-steroid system. Reactions are described and physical evidence is presented which establish the constitution and configuration of the isoxazolidine-containing cycloaddition products, and the mechanistic and steric course of this transannular ring closure process is discussed.

Lead tetra-acetate oxidation of saturated aliphatic alcohols—V : Factors influencing the formation of cyclic ethers and carbonyl compounds☆☆☆

Abstract Factors influencing the relative rates of the homolytic and heterolytic processes in the lead tetra-acetate oxidation of unbranched primary and secondary aliphatic alcohols have been investigated, with a view to determine the conditions giving optimal yields of cyclic ethers or carbonyl compounds.

Configurational and conformational studies of some B-homo-A-nor-steroids☆☆☆

Abstract Cyclization of (E)-3β-hydroxy-5,10-seco-cholest-1(10)-en-5-one acetate (1) by treatment with H⊕ in aprotic solvents leads to a mixture of two 1,5-stereoisomeric 5(10 → 1)abeo-cholest-10(19)-ene-3β,5-diol 3-acetates 2 (major product) and 3, whereas the thermal cyclization of 1 affords exclusively product 2. On the basis of chemical transformations and interpretation of physical measurements, particularly of CD data of 5-membered and 7-membered ring ketones derived from products 2 and 3, it was possible to assign the trans 1β,5α-configuration to the 5(10 → 1)abeo-steroid 2, and the cis 1α,5α-configuration to the stereoisomeric product 3. The stereochemical course of these cyclization reactions is discussed in terms of possible transition state (and ground state) conformations of the trans-cyclodecene ring in the starting 5,10-seco-1(10)-en-5-one 1 (and its protonated intermediate).

Opening of steroid ring a by means of lead tetraacetate

Abstract The lead tetraacetate oxidation of cholestan-1β-ol and cholestan-1α-ol in benzene solution did not afford cyclic ethers but resulted, in major part, in the opening of ring A with formation of 1,10-seco-aldehydes. In addition, cholestane, cholest-1-ene and cholestan-1-one were also obtained.

A novel procedure for the aromatization of ring a in 19-nortestosterone

Abstract A convenient, 40% overall yield synthesis of 2,3,17β-triacetoxy-1,3,5(10)-estratriene is described, which involves epoxidation of 19-nortestosterone and subsequent acetylation, lead tetra-acetate acetoxylation of the so-formed 17β-acetoxy-4β,5-epoxy-5β-estran-3-one, and aromatization of ring A, by means of acidic alumina, of the resulting 2α and 2β epimers of 2,17β-diacetoxy-4β,5-epoxy-5β-estran-3-one.