A Mild Synthesis of Vinyl Halides and<i>gem</i>-Dihalides Using Triphenyl Phosphite−Halogen-Based Reagents

Spaggiari, Alberto; Vaccari, Daniele; Davoli, Paolo; Torre, Giovanni; Prati, Fabio

doi:10.1021/jo061346g

Cited by 105 publications

(65 citation statements)

References 51 publications

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“…Use of excess PCl 5 produced only poly-chlorinated products having the general structure 70 while leaving the ketone moiety untouched. Treatment of 39 with other electrophilic chlorine reagents known to effect conversion of ketones into vinyl chlorides, such as PPh 3 /CCl 4 32 and P(OPh) 3 /Cl 2 , 33 also failed to deliver the desired vinyl chloride, and dichlorination of the indole ring was again observed. When the more oxophilic reagent WCl 6 was employed, 34 a complex mixture was obtained.…”

Section: Resultsmentioning

confidence: 99%

Studies toward welwitindolinones: formal syntheses of N-methylwelwitindolinone C isothiocyanate and related natural products

McElroy

Shamszad

et al. 2013

Tetrahedron

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Section: Resultsmentioning

confidence: 99%

Studies toward welwitindolinones: formal syntheses of N-methylwelwitindolinone C isothiocyanate and related natural products

McElroy

Shamszad

et al. 2013

Tetrahedron

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“…In the case of 10-undecenoyl amides ( Table 1, entries [11][12][13][14], benzhydryl amide 1m was converted into 10-undecenenitrile in excellent yield (entry 13), whereas N-tertbutyl, N-benzhydryl, and N,N-dibenzyl amides (1k,l,n) gave only moderate yields (entries 11, 12, and 14).…”

Section: Equationmentioning

confidence: 99%

“…12 In particular, amides 1a-x were treated at -60°C with a freshly prepared solution of TPPBr 2 in chloroform in the presence of triethylamine; in the case of tertiary amides, triethylamine was not included. After warming to room temperature, the reaction mixture was gently refluxed overnight to achieve complete conversion, when necessary, and the crude residue was purified by column chromatography.…”

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confidence: 99%

A Mild Synthesis of Nitriles by von Braun Degradation of Amides Using Triphenyl Phosphite-Halogen-Based Reagents

Vaccari¹,

Davoli²,

Spaggiari³

et al. 2008

Synlett

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A mild procedure for the synthesis of aromatic and aliphatic nitriles is disclosed. In the presence of bromotriphenoxyphosphonium bromide (TPPBr 2 ), N-alkyl and N,N-dialkyl amides undergo von Braun degradation to nitriles in good to excellent yields under the mildest conditions ever reported. The reaction proceeds via formation of an iminoyl bromide intermediate at -60°C, which subsequently dealkylate upon refluxing in chloroform or even at room temperature. In the case of N-tert-butyl, N-a-phenylethyl and N-benzhydryl amides, chlorotriphenoxyphosphonium chloride (TPPCl 2 ) generated at -30°C was also effective.Since the first nitrile synthesis reported by Wöhler and von Liebig as early as 1832, 1 a great deal of research has been devoted to the development of efficient and straightforward processes for the preparation of organic cyanides. 2 Nitriles, in fact, play an important role in organic synthesis as useful substrates for a variety of transformations, and their relevance has increased accordingly along the years. 3 Most recently, nitriles have even featured as partners in alkyne metathesis. 4Dealkylation of secondary and tertiary benzamides upon heating in the presence of halogenating reagents is traditionally referred to as the von Braun degradation. Namely, when N-alkyl and N,N-dialkyl amides are treated with inorganic phosphorus halides or thionyl chloride, decomposition into a nitrile and alkyl halide(s) occurs. 5,6 The reaction requires harsh conditions (typically 90-150°C) and, in addition, the resulting products need to be isolated by distillation from the crude reaction mixture, owing to the formation of otherwise intractable phosphoric tars and byproducts. Because of these drawbacks, the von Braun degradation has found relatively little use for the preparation of nitriles sensu stricto, and applications have mainly focused on the alkyl halide product(s) instead, especially for structure elucidation purposes in the alkaloid field. 7 Although slight modifications have been proposed, 8 the reaction conditions still remain quite aggressive, and have limited the usage of this process for synthetic applications. Clearly, if milder reaction conditions were available, the synthetic scope of the von Braun degradation could be extended and the reaction would gain a renewed appeal for the preparation of nitriles.Recently, we have exploited halotriphenoxyphosphonium halides, viz. (PhO) 3 P + X X -(henceforth TPPX 2 , where X = Cl or Br), for the activation of a variety of amides into the corresponding iminoyl halides; this has resulted in the development of exceedingly mild protocols for the deacylation of secondary amides, 9a,b for the synthesis of nitrogen-containing heterocycles such as b-carbolines 9c and pyrroles, 9d and also for the dehydration of primary amides into nitriles. 9eBy close analogy, we envisaged that the remarkable halogenating potential of TPPX 2 could be exploited also in the framework of a von Braun degradation which is well known to proceed via an imidoyl halide intermediate. 6b,10 I...

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“…Vinyl halides, in particular, are versatile substrates in many useful organic transformations including the well-known Stille, Suzuki, and Sonogashira coupling reactions [4][5][6][7][8][9][10]. The importance of vinyl halides in organic synthesis has stimulated a great deal of interest and much attention has been devoted to the synthesis of vinyl halides and their derivatives [11][12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Regio- and stereospecific synthesis of vinyl halides via carbozincation of acetylenic sulfones followed by halogenation

Xie¹,

Wang²,

Zhang³

et al. 2009

Journal of Organometallic Chemistry

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A Mild Synthesis of Vinyl Halides andgem-Dihalides Using Triphenyl Phosphite−Halogen-Based Reagents

Cited by 105 publications

References 51 publications

Studies toward welwitindolinones: formal syntheses of N-methylwelwitindolinone C isothiocyanate and related natural products

Studies toward welwitindolinones: formal syntheses of N-methylwelwitindolinone C isothiocyanate and related natural products

A Mild Synthesis of Nitriles by von Braun Degradation of Amides Using Triphenyl Phosphite-Halogen-Based Reagents

Regio- and stereospecific synthesis of vinyl halides via carbozincation of acetylenic sulfones followed by halogenation

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