Synthesis of phenoxathiins using an iron-catalysed C-H thioarylation

Phenoxathiins are an important class of sulfur-containing heterocycle, found as the core component in numerous pharmaceutically active agents and materials. Despite this importance, there are relatively few methods for the synthesis of these heterocycles that avoid complex starting materials, harsh conditions or precious transition metals. We report a two-step synthesis of phenoxathiins from phenols using iron and copper-mediated reactions. The first step involves the accelerated ortho-thioarylation of phenols using N-(2-bromophenylthio)succinimide, catalysed by the Lewis acid, iron(III) triflimide and the Lewis base, bis(4-methoxyphenyl)sulfane. In the second step, the thioarylated products were converted to a series of phenoxathiins using a copper-mediated, Ullmann-type, C-O bond forming cyclisation reaction. The synthetic utility of this two-step approach for the preparation of biologically relevant phenoxathiins was demonstrated using natural product-based phenols.

Synthesis and Characterization of Hybrid Dimeric Steroid Spiroketals

The synthesis of six dimeric spiroketals bearing an estradiol half fused to the 5α- or 5β-epimers of androstane, cholestane, and spirostane nuclei is described. The synthetic procedure comprises the Sonogashira­ coupling of different steroid alkynes with 2-iodoestradiol 17-monoacetate, followed by Pd-catalyzed spiroketalization. The structural characterization of the obtained hybrid dimers was performed using a combination of 1D and 2D NMR techniques, and was assisted by DFT calculations. Single crystal X-ray diffraction of one of the obtained compounds confirmed the proposed structures.

Combined epimerisation and acylation: Meerwein–Ponndorf–Verley–Oppenauer catalysts in action

A practical racemisation-epimerisation method for chiral secondary alcohols has been developed. Meerwein-Ponndorf-Verley-Oppenauer catalysts such as neodymium(III) isopropoxide are able to racemise these alcohols with retention of other stereocentres in the molecule. This is particularly useful for the recycling of the undesired products of kinetic resolutions of alcohols. By combination of such a racemisation with an acylation using isopropenyl or ethoxyvinyl esters as acyl donors, a fast straightforward recycling of starting materials may be achieved. The combined epimerisation and acylation process is demonstrated for the steroid estradiol methyl ether.

Effect of 11 beta-substituents on the regioselective chlorination of estrogens with 2,3,4,5,6,6-hexachloro-2,4-cyclohexadienone

The reaction of 11 beta-substituted estrogens with 2,3,4,5,6,6-hexachloro-2,4-cyclohexadienone affords exclusively ortho-substituted monochlorinated products including a major 4-chloro and a minor 2-chloro derivative. In the absence of an 11 beta-substituent, regioselectivity is lost, resulting in a mixture of 10 beta- and ortho-chlorinated products.

The synthesis of estriol 16- and 17-monoglucuronide from estriol

An efficient and convenient procedure for the synthesis of estriol 16- and 17-monoglucuronides from estriol is described. This is achieved by the selective protection and deprotection of the hydroxy groups in estriol, Koenigs-Knorr reactions with methyl 1-bromo-1-deoxy-2,3,4-tri-O-acetyl-alpha-D-glucopyranuronate and subsequent hydrolysis. The products have been characterized by proton nuclear magnetic resonance (1H NMR), two-dimensional 1H homonuclear shift-correlated spectra (2D-COSY) and mass spectra. The selective Koenigs-Knorr reaction of the alcoholic hydroxyl group in the presence of a phenolic hydroxyl group is also reported.

Regioselective A-ring iodination of estradiol diacetates

Treatment of estrone or estradiol acetate with thallium trifluoroacetate in TFA and subsequent reaction with KI gave the 2-iodoestrogens as the major product. In the case of estradiol diacetate, treatment of the thallation product with [125I]NaI, using the same reaction conditions, gave exclusively the 2-iodo isomer. Thus, regioselectivity combined with rapidity, renders this procedure particularly suitable for A-ring radioiodination of estradiol with short-lived isotopes.