Synthesis of triaromatic steroid hydrocarbons methylated at position 2, 3 or 6: molecular fossils of yet unknown biological origin

A bioinspired approach for construction of the [7-5-6-5] all-carbon tetracyclic core of logeracemin A

An efficient successive Michael/double aldol/dehydration reaction approach for the spiro-linked DEFF′ tetracyclic core ring systems of logeracemin A was developed.

An Acid-Catalyzed Addition and Dehydration Sequence for the Synthesis of Heteroarylated Steroidal Dienes

Additions of heteroarenes to hormone steroids containing an α,β-unsaturated ketone are reported. Additions of a range of electron-rich heteroarene nucleophiles, including indoles, a pyrrole, and a thiophene, to a variety of commercially available steroids and subsequent dehydration formed 3-heteroarylated steroidal dienes in up to 93% yield. This atom-economical reaction sequence occurs under mild reaction conditions in the presence of catalytic bismuth triflate.

Transformations of 3-hydroxy steroids with lewis and anhydrous protic acids: the case of pregn-4-en-3β,17α,20β-triol

The acid-catalyzed dehydration is one of the most important processes, which transforms 3-hydroxy steroids into their corresponding unsaturated derivatives. This reaction is of great importance because it can produce molecules that play a key role in the understanding of the natural metabolism of steroids. Sterol dehydration is generally performed with aqueous acidic systems, and the treatment often affords low yields of the desired compounds and/or complex mixtures of by-products. In this paper, we report the results obtained from the study of the structural and stereochemical effects of the acid-induced reaction of pregn-4-en-3β,17α,20β-triol in anhydrous systems. In particular, the treatment of this trihydroxy steroid model with Lewis acids leads to the corresponding Δ(3,5) -steradiene as the only product and in very high yields. With Lewis acids, no modifications of the 1,2-diol function on the D-ring are observed, even when the reactions are performed at high temperatures. Protic acid catalysis in non-aqueous organic solvents causes the formation of an epimeric mixture of the corresponding Δ(3,5) -steradiene derivatives by a partial stereochemical inversion of the asymmetric C-17. The reactivity of the 17α,20β-diolic residue is also evaluated by exposing pregn-4-en-3β,17α,20β-triol and the corresponding Δ(3,5) -steradiene to the prolonged action of anhydrous protic acid systems under thermal conditions.

Natural aromatic steroids as potential molecular fossils from the fruiting bodies of the ascomycete Daldinia concentrica

The identification of aromatic steroid hydrocarbons bearing a methyl group at positions 1, 2, 3, 4, or 6 in sediments and petroleum has been puzzling since possible steroidal precursors have not yet been reported in living organisms. Two new aromatic steroids, (17beta,20R,22E,24R)-19-norergosta-1,3,5,7,9,14,22-heptaene (1) and (17beta,20R,22E,24R)-1-methyl-19-norergosta-1,3,5,7,9,14,22-heptaene (2), were isolated from the ascomycete Daldinia concentrica, of which compound 2 bears an unusual methyl group at position 1. We propose that the origin of these compounds is derived from the transformation undergone by their precursor due to microbial action. Compounds 1 and 2 could be the long-sought, biological precursor steroids for organic matter in Earth's subsurface.