Allylic rearrangement of cyanophosphates. III Reaction of acyclic enone cyanophosphates.

N-Heterocyclic carbenes prepared from imidazolium salts and bases, have been used mainly in transition metal-catalyzed reactions as ligands.1,2) However, their suitability as nucleophilic catalysts has been underdeveloped. [3][4][5][6][7][8][9][10][11] We recently reported a catalytic method leading to the synthesis of various cyanohydrins using N-heterocyclic carbene 2 prepared from 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (1) and KOt-Bu as a nucleophilic catalyst in cyanosilylation reactions.12) Cyanohydrins and their trimethylsilyl ethers are versatile intermediates in organic synthesis, 13,14) but the instability of cyanohydrins and their trimethylsilyl ethers is sometimes problematic for further transformations. Therefore, the development of a one-pot cyanation-O-protection reaction with a stable protecting group is desirable. In 1983, the above one-pot reaction of carbonyl compounds with diethyl cyanophosphonate (DEPC) in the catalytic amount of lithium diisopropylamide has been reported by Shioiri et al. 15) Herein, we disclose the first catalytic method leading to the synthesis of various cyanohydrin-O-phosphonates using N-heterocyclic carbene 2 prepared from 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (1) and KOt-Bu as a nucleophilic catalyst in cyano-phosphorylation reactions.The cyano-phosphorylation of various aldehydes 3-10 was performed as shown in Table 1. The aldehydes except for trans-cinnamaldehyde (9) were reacted with N-heterocyclic carbene 2 prepared from 5 mol% of the imidazolium chloride 1 and 4 mol% of KOt-Bu, and 1.2 mol eq of DEPC in THF, affording the corresponding cyanohydrin-O-phosphonates in good yields.16) A polar solvent such as DMF was also a suitable solvent (entry 5). The use of ketones such as acetophenone and methyl vinyl ketone afforded little or none of the desired products.In summary, N-heterocyclic carbene 2 was found to function as catalyst in cyano-phosphorylation reaction of aldehydes with DEPC. Ongoing efforts are focused on developing an asymmetric version 17,18) of this reaction with a chiral Nheterocyclic carbene. ExperimentalIR spectra were measured on a JASCO IR Report-100 diffraction grating IR spectrophotometer.1 H-(270 MHz) and 13 C-NMR (68 MHz) spectra were measured on a JEOL JNM-EX-270 NMR spectrometer. MS spectra were measured on a JEOL JMS-SX-102A instrument. Commercially available aldehydes and reagents were used without any purification. THF was distilled from Na/benzophenone ketyl under a nitrogen atmosphere. DMF was distilled from CaH 2 under reduced pressure. Silica gel column chromatography was performed on Fuji silysia PSQ 60B.Representative Procedure for the Cyano-Phosphorylation Reaction To a stirred solution of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride (1) (5.1 mg, 15 mmol) in THF (1.0 ml) was added KOt-Bu (1.4 mg, 13 mmol) at rt and the mixture was stirred for 15 min at the same temperature. After dissolving the imidazolium chloride 1 completely, the mixture was cooled to 0°C. Then, benzaldehyde (6) (32.1 mg, 0.302 m...

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“…19) Phosphoric acid 1-cyano-3-phenyl-allyl ester diethyl ester. 21) Phosphoric acid 1-cyano-allyl ester diethyl ester. …”

Section: Methodsmentioning

confidence: 99%

Cyano-Phosphorylation of Aldehydes Catalyzed by a Nucleophilic N-Heterocyclic Carbene

Fukuda

Maeda

Kondo

et al. 2006

CHEMICAL & PHARMACEUTICAL BULLETIN

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“…Meanwhile, in the case of 4-methoxy-, 8 4-(trifluoromethoxy)-, and 2,4-dimethoxybenzaldehyde, furan-3-carbaldehyde, and indole-3-carbaldehyde, 9 the corresponding CPs could not be isolated, owing to the elimination of phosphate anion prompted by their donating groups.…”

Section: Table 1 Conversion Of 4-isobutylbenzaldehyde C...mentioning

confidence: 99%

Transformation of Benzaldehydes to Benzonitriles via Cyanophosphates without One-Carbon Homologation

Yoneyama,

Okada,

Hayama

et al. 2024

Synthesis

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Transformation of benzaldehydes to benzonitriles via cyanophosphates (CPs) with tetrabutylammonium azide (Bu4N·N3) was found, affording a range of benzonitriles in modest-to-high yields. As the CN-carbon of benzonitriles arises from the formyl-carbon of benzaldehydes, this is a new type of CP-reaction, distinctly different from the past one-carbon nitrile homologation. In contrast, reaction of ketone- or aliphatic aldehyde-CPs with Bu4N·N3 occurred mono-deethylaton, forming tetrabutylammonium salts.

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“…Related [3,3] rearrangements have however precedence in the isomerization of allylic phosphates. [12] The driving force for the formation of D is the creation of a new PÀO bond and the formation of a relatively stable vinyl carbanion. Furthermore, intermediate D is kinetically stabilized as the final E2 elimination to form 6 requires an s-trans arrangement of the vinyl lone pair and the phosphate leaving group.…”

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confidence: 99%

Mechanism of the Phospha‐Wittig–Horner Reaction

et al. 2013

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Phosphaalkenes are prominent ligands in homogenous catalysis due to their p-acceptor capacity [1] and are appealing building blocks in polymer science. [1b, 2] Methods for their preparation are however often limited by small substrate scopes, or residual OTMS substituents that stem from certain synthetic methods.[3] The phospha-Wittig-Horner (pWH) reaction, as first coined by Mathey and co-workers, [4] converts aldehydes and relatively unreactive ketones into C-monoand C,C-disubstituted phosphaalkenes, respectively (Scheme 1, top). Furthermore, the substituent at the phosphorus center can be chosen rather freely, although smaller groups demand additional stabilization by metal coordination.[5] In context of our previous work on the incorporation of low-valent phosphorus into unsaturated carbon scaffolds, [6] we were interested to see whether the scope of the pWH reaction could be extended to ketene substrates from which 1-phosphapropadienes would become accessible. Such phosphaallenes are the shortest members of an intriguing class of P-terminated cumulenes, which have however been synthetically highly challenging with only sporadic reports in the literature. [7] Despite of the synthetic versatility of the pWH reaction, it has been a greatly underexplored method for the preparation of phosphaalkenes. At the same time, the reaction mechanism has hitherto been unknown. Formally, the pWH reaction is the phosphorus analogue to the Horner-WadsworthEmmons reaction (HWE), which allows preparation of alkenes and allenes from carbonyl compounds and ketenes, respectively.[8] The mechanism of the HWE reaction has been studied in great detail over the last decades, with the crucial step being a simultaneous CÀP and CÀO bond cleavage in an intermediately formed oxaphosphetane to afford the desired alkene and the phosphate byproduct (Scheme 1, bottom).[9] In the spirit of the frequently drawn analogy between phosphorus and carbon, [10] it was assumed that the pWH reaction proceeds along a similar pathway. In the present report, we show for the first time that this assumption is wrong and that the pWH reaction proceeds in a more complex, stepwise fashion. The mechanism of the pWH reaction is elucidated with the aid of spectroscopically and crystallographically characterized reaction intermediates.The present study is based on two pWH reagents that are stabilized by {W(CO) 5 } fragments but differ in the P III substituent (1, 2), [5a] and two substrate ketenes, one with phenyl substituents (3), the other with a fused fluorenyl core (4). As for all HWE and pWH reactions, the reactions are initiated by the addition of base. Thus, stoichiometric amounts of organic base (1,8-diazabicyclo[5.4.0]undec-7-ene, DBU) were added to 1 or 2 followed by the addition of either ketene 3 or 4. The products that were obtained after 30 min and aqueous workup were however not the expected phosphaallenes, but previously unknown phosphinophosphates 5 a-d (Scheme 2).Complexes 5 a-d are obtained as pale yellow solids in good to excellent yields. The...

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Allylic rearrangement of cyanophosphates. III Reaction of acyclic enone cyanophosphates.

Cited by 18 publications

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Cyano-Phosphorylation of Aldehydes Catalyzed by a Nucleophilic N-Heterocyclic Carbene

Cyano-Phosphorylation of Aldehydes Catalyzed by a Nucleophilic N-Heterocyclic Carbene

Transformation of Benzaldehydes to Benzonitriles via Cyanophosphates without One-Carbon Homologation

Mechanism of the Phospha‐Wittig–Horner Reaction

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