Oxidative Coupling Reactions Mediated by MoCl₅ Leading to 2,2′‐Cyclolignans: The Specific Role of HCl

Abstract

The scope and performance of oxidative coupling reaction using MoCl 5 can be significantly improved by employing Lewis-acidic additives such as TiCl 4 , SnCl 4 , or SiCl 4 . Since the by-product, HCl, plays a particular function as an inhibitor for MoCl 5 by forming chloro complexes, exploiting typical chloride scavengers, like silver salts or molecular sieves, is also successful. A variety of differently substituted 1,4-diarylbutanes 4a−g, which were easily synthesized by a modular approach, were

Synthetic Applications of Oxidative Aromatic Coupling—From Biphenols to Nanographenes

“…However, for highly electron‐rich substrates or when the coupling process proceeds slowly, chlorination becomes an issue . The application of MoCl 5 together with a Lewis acid (usually TiCl 4 ), which is believed to bind the coformed chloride anions, increases the overall efficiency of the C−C coupling, but this beneficial effect is not general. To solve this problem, the Waldvogel group designed the two dinuclear molybdenum(V) complexes 1 and 2 (Figure ), which were prepared from MoCl 5 and either 1,1,1,3,3,3‐hexafluoroisopropanol (HFIP) or 2,2,2‐trifluoroethanol (TFE) in 95 % and 97 % yield, respectively.…”

Oxidative Coupling Reactions of 1,3‐Diarylpropene Derivatives to Dibenzo[a,c]cycloheptenes by PIFA

“…[11][12][13] The performance of this reagent can be enhanced when Lewis acids are used to bind hydrogen chloride. [14] If α-benzylcinnamic acid derivatives 2 are subjected to this reagent mixture, overoxidation occurs, and an oxidative domino coupling follows resulting in the formation of 1 (Scheme 1). An intermediate tropylium species is postulated, which allows the installation of a carbon side chain.…”

Oxidative Coupling of Diaryldisulfides by MoCl5 to Thianthrenes

“…[23] For oxidative cyclization reactions Lewis acidic additives can be beneficial since they act as HCl trapping agents. [24] The required starting materials disulfides can either be purchased or are accessible by various standard oxidations, [25] Among those, the treatment with iodine/pyridine turned out to be the most practical. Only the optimized reaction conditions for the oxidative coupling products are depicted (Table 1).…”