Reinvestigation of Highly Diastereoselective
Pentacyclic Spirolactone Formation by Direct Anodic Oxidation
of 2,4-Dimethylphenol

Barjau, Joaquin; Königs, Pia; Kataeva, О. N.; Waldvogel, Siegfried R.

doi:10.1055/s-2008-1078276

Cited by 16 publications

(8 citation statements)

References 1 publication

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“…14, purple). Although this group of by-products is mainly formed under basic conditions [61][62][63][64][65] to a smaller extent it is also formed in the electrolyte system used here. The third class are linear coupling products of 4, including the diphenyl ether of 4 (Fig.…”

Section: Analysis Of By-products Occurring During the Electrolysis Ofmentioning

confidence: 99%

“…The electrosynthetic approach to 5 was a major field of Waldvogel group within the past decades [48,61]. Under most conditions this particular substrate 4 is very prone to side reactions and forms polycyclic products in a broad structural diversity [62][63][64][65]. Consequently, a boron-templated anodic process was established which provides good yields even on multi-kg scale [66,67].…”

Section: Introductionmentioning

confidence: 99%

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Electrosynthesis of 3,3′,5,5’-Tetramethyl-2,2′-biphenol in Flow

et al. 2020

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Abstract3,3′,5,5’-Tetramethyl-2,2′-biphenol is well known as an outstanding building block for ligands in transition-metal catalysis and is therefore of particular industrial interest. The electro-organic method is a powerful, sustainable, and efficient alternative to conventional synthetic approaches to obtain symmetric and non-symmetric biphenols. Here, we report the successive scale-up of the dehydrogenative anodic homocoupling of 2,4-dimethylphenol (4) from laboratory scale to the technically relevant scale in highly modular narrow gap flow electrolysis cells. The electrosynthesis was optimized in a manner that allows it to be easily adopted to different scales such as laboratory, semitechnical and technical scale. This includes not only the synthesis itself and its optimization but also a work-up strategy of the desired biphenols for larger scale. Furthermore, the challenges such as side reactions, heat development and gas evolution that arose during optimization are also discussed in detail. We have succeeded in obtaining yields of up to 62% of the desired biphenol.

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Section: Analysis Of By-products Occurring During the Electrolysis Ofmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Electrosynthesis of 3,3′,5,5’-Tetramethyl-2,2′-biphenol in Flow

et al. 2020

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“…In the course of their studies on the synthesis of 2,2’-biphenols via anodic coupling of phenols [78–79], they could observe the formation of spiropentacyclic scaffold 76 (Scheme 29) as byproduct of the electrolysis of 2,4-dimethylphenol ( 72 ) [80]. Later it turned out that compound 73 (a dehydrotetramer of 72 ) is the actual electrolysis product, which reacted to 76 via thermal rearrangement under loss of a phenol unit during purification of the crude product by sublimation [81]. The authors proposed a mechanism where the formation of 73 starts with the anodic generation of a derivative of Pummerer’s ketone ( 74 ) from two phenol units.…”

Section: Reviewmentioning

confidence: 99%

“…Since spiropentacycle 76 resembles the core moieties of several natural products and therefore seemed to be a useful starting point for further investigations [81], the authors decided to optimize the reaction conditions in favor of the formation of 73 . As optimum reaction conditions, the use of a Ba(OH) 2 /MeOH electrolyte in combination with platinum electrodes and a current density of 12.5 mA/cm 2 was identified.…”

Section: Reviewmentioning

confidence: 99%

Recent advances in the electrochemical construction of heterocycles

Francke

2014

Beilstein J. Org. Chem.

118

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SummaryDue to the fact that the major portion of pharmaceuticals and agrochemicals contains heterocyclic units and since the overall number of commercially used heterocyclic compounds is steadily growing, heterocyclic chemistry remains in the focus of the synthetic community. Enormous efforts have been made in the last decades in order to render the production of such compounds more selective and efficient. However, most of the conventional methods for the construction of heterocyclic cores still involve the use of strong acids or bases, the operation at elevated temperatures and/or the use of expensive catalysts and reagents. In this regard, electrosynthesis can provide a milder and more environmentally benign alternative. In fact, numerous examples for the electrochemical construction of heterocycles have been reported in recent years. These cases demonstrate that ring formation can be achieved efficiently under ambient conditions without the use of additional reagents. In order to account for the recent developments in this field, a selection of representative reactions is presented and discussed in this review.

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“…Consequently, usually a complex mixture of several products are formed within the oxidation process (Scheme 1). 18,19 Especially noteworthy byproducts are some pentacyclic scaffolds like 7-10, whereby 9 and 10 represent secondary products of dehydrotetramer 7. 14,20 Depending on the con-ditions of the electrolysis different products can be dominant.…”

mentioning

confidence: 99%

Selective and Scalable Dehydrogenative Electrochemical Synthesis of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

Selt

Mentizi

Schollmeyer

et al. 2019

Synlett

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3,3′,5,5′-Tetramethyl-2,2′-biphenol is a compound of high technical significance, as it exhibits superior properties as building block for ligands in the transition-metal catalysis. However, side reactions and overoxidation are challenging issues in the conventional synthesis of this particular biphenol. Here, an electrochemical method is presented as powerful and sustainable alternative to conventional chemical strategies, which gives good yields up to 51%. Despite using inexpensive and well-available bromide-containing supporting electrolytes, the issue of bromination and general byproduct formation is effectively suppressed by adding water to the electrolyte. Additionally, the scalability of this method was demonstrated by conducting the electrolysis on a 122 g scale.

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Reinvestigation of Highly Diastereoselective Pentacyclic Spirolactone Formation by Direct Anodic Oxidation of 2,4-Dimethylphenol

Cited by 16 publications

References 1 publication

Electrosynthesis of 3,3′,5,5’-Tetramethyl-2,2′-biphenol in Flow

Electrosynthesis of 3,3′,5,5’-Tetramethyl-2,2′-biphenol in Flow

Recent advances in the electrochemical construction of heterocycles

Selective and Scalable Dehydrogenative Electrochemical Synthesis of 3,3′,5,5′-Tetramethyl-2,2′-biphenol

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