Über Steroide und Sexualhormone. 211. Mitteilung. Direkte Einführung einer Sauerstoffunktion in die Methylgruppe C‐18 im intakten Steroidgerüst

Abstract

Treatment of 3β‐acetoxy‐20β‐hydroxy‐5α‐pregnane (11) with lead tetraacetate in benzene allows the selective introduction of an oxygen function at the no11 activated angular methyl group C‐18. The main product of this reaction is the 18,20β‐oxido compound I11 as proved by its conversion into the lactone V and the lactol VI.

Pyridinium Salts as Redox‐Active Functional Group Transfer Reagents

“…As first demonstrated by Jeger,A rigoni, and co-workers, alkoxy radicals bearing hydrogen atoms in the d-position readily undergo intramolecular 1,5-HAT, thus enabling the site-selective functionalization of non-activated remote CÀH bonds. [81] Thea bility to generate oxygen-centered radicals in complex molecules for remote functionalization is particularly intriguing due to the ubiquitous nature of hydroxy groups in organic molecules.R ecently,p hotoredox catalysis has emerged as ap romising technique for the generation of oxygen-centered radicals from functionalized or free alcohols. [82,83] Alternatively, N-alkoxy pyridinium salts can be readily accessed from the corresponding alcohol by atwo-step procedure involving conversion into al eaving group and asubsequent substitution reaction with pyridine N-oxide.…”

Dual Photoredox/Copper Catalysis for the Remote C(sp3)−H Functionalization of Alcohols and Alkyl Halides by N‐Alkoxypyridinium Salts

“…Since Arigoniss eminal paper on the remote functionalization of unactivated C(sp 3 ) À Hbond involving in situ generated alkoxy radicals, [1] several synthetically useful protocols have been developed with the classic Barton reaction of alkyl nitrites (RONO) being the most influential. [2] Mechanistically,homolytic cleavage of the OÀXorOÀmetal bonds under photolysis or thermal conditions would generate the alkoxy radical A.R egioselective 1,5-hydrogen atom transfer (1,5-HAT) would afford the carbon radical B which, upon abstraction of the XC from the starting material, would furnish the d-C(sp 3 )ÀHf unctionalized product with concurrent regeneration of the alkoxy radical A to propagate the radical chain process (Scheme 1a).…”

Formal Total Synthesis of (−)-Jiadifenolide and Synthetic Studies toward seco-Prezizaane-Type Sesquiterpenes

“…32 yield. 38 The byproduct 58, bearing an additional acetyl group at the carbon next to the ether, 39 was further isolated and successfully converted to the desired product 57 using BF 3 . OEt 2 and triethylsilane.…”