Krzysztof Błaszczyk

A new approach to the synthesis of the 17β-butenolide fragment of cardenolides

Abstract A new, efficient synthesis of the 17β-butenolide fragment characteristic of cardenolides is effected by [2 + 2]-cycloaddition of dichloroketene to 3β-acetoxypregna-5,20-diene, as a key step.

Steroidal cyclobutanones. Part 2. Diastereofacial selection in the cycloaddition of dichloroketene and 3β-acetoxy-20a-homopregna-5,20-diene. Crystal structure of the cycloadduct, (20S)-3β-acetoxy-20,24-cyclo-22,22-dichlorochol-5-en-23-one

The reaction of dichloroketene and 3β-acetoxy-20a-homopregna-5,20-diene 1 is shown to give one diastereoisomeric cycloadduct 2 arising from attack at the rear side of the preferred rotamer 1b of the steroid skeleton. The structure of dichlorocyclobutanone 2 was determined by X-ray crystallography. Reduction of 2 gives chlorocyclobutanone 3 and cyclobutanone 4. Examination of the cyclobutanones by CD, 1H and 13C NMR spectroscopy demonstrates that these techniques can be used for the determination of the configuration of 2 and 3.

Steroidal cyclobutanones@@@Steroid-Cyclobutaneone (Kurz Mitteilung): Short communication

Cycloaddition of dichloroketene and 3-, 7-, 17-, and 20-methylene steroids affords the corresponding cyclobutaneones in yields reflecting the steric crowding around the reacting olefinic double bond.ZusammenfassungCycloaddition von Dichlorketen an 3-, 7-, 17- und 20-Methylen-Steroide ergab die jeweiligen Cyclobutanonderivate in Ausbeuten, die den sterischen Gegebenheiten rund um die reagierenden olefinischen Doppelbindungen entsprechen.

A novel synthetic approach to (20R)- and (20S)-21-hydroxy steroids. Synthesis of a marine sterol 21-hydroxycholesterol.

A short and efficient synthesis of steroid synthons, di(tert-butyldimethylsilyl) ethers of 3,21-dihydroxy-24-nor-chol-5-en-23-al (8 and 10) and of ethyl 3,21-dihydroxy-25-homo-chola-5,23-dien-25-oate (9 and 11), having natural (20R) and unnatural (20S) configuration from 3β-(tert-butyldimethylsilyloxy)-14α,20ξ-card-5-enolide (2) is reported. Further elongation of the side chain of these synthons provides a new method for the synthesis of (20R) and (20S)-21-hydroxy steroids. The utility of the method was exemplified by the synthesis of a natural marine sterol - 21-hydroxycholesterol (18).

1H and13C NMR Data for Spiro Steroids, Derivatives of 5α-Cholestane

1H and 13C NMR spectral data for 18 spiranes, derivatives of 5α‐cholestane, are reported. The relationship between the configuration of the spirane carbon atom and the positions of 1H and 13C chemical shifts of the spirane moiety is presented.