Evidence of Formation of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Carbon Nucleophiles

Brunel, Jean Michel; Maffei, Michel; Muchow, Günter; Buono, Gérard

doi:10.1002/(sici)1099-0690(200005)2000:9<1799::aid-ejoc1799>3.0.co;2-b

Cited by 6 publications

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References 28 publications

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“…[6] This demonstration has been realized performing numerous NMR experiments and by X-ray structure analysis. Thus, the almost exclusive formation of the endo-disubstituted spirocyclopropane compound 2b under the appropriate conditions underlines that the reaction proceeds through an exo-(π-allyl)palladium complex.…”

Section: Resultsmentioning

confidence: 99%

“…Last year, we reported the evidence of formation of an exo-(π-allyl)palladium intermediate in the Pd 0 -catalyzed alkylation of bicyclic allylic diacetate 1 with stabilized nucleophiles (Scheme 1). [6] Scheme 1. Pd 0 -catalyzed alkylation of allylic bicyclic diacetate 1 [a] Recently, our results have been the subject of a comment by Lloyd-Jones suggesting that only a mixture of isomers of 2a and 2b is obtained without evident proof on the exact structure of these compounds and that the mechanism is not well discussed.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Evidence on the Existence of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Nucleophiles

Brunel¹,

Maffei²,

Muchow³

et al. 2001

Eur. J. Org. Chem.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Evidence on the Existence of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Nucleophiles

Brunel¹,

Maffei²,

Muchow³

et al. 2001

Eur. J. Org. Chem.

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On the Evidence for Formation of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate

Lloyd‐Jones

2001

Eur. J. Org. Chem.

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The elucidation of the relative or absolute stereochemistry [1] of reaction products and subsequent inferences on the mechanism or mechanisms of reaction is a fundamental tool in both modern and classical physical organic chemistry. The stereochemical intricacies of Pd-catalysed allylic alkylation [2] are now known to a sufficient extent that the products of such reactions can, in suitable cases, be studied to deduce the stereochemistry of π-allylϪPd intermediates. [3] In most cases [4] Pd-catalysed allylic alkylation proceeds via an inversionϪinversion sequence, resulting in overall retention of stereochemistry. [5] The last half of this overall sequence, involving nucleophilic attack anti to the palladium in the π-allyl complex, was recently employed by Buono et al., [6] to probe the stereochemistry of the Pd-catalysed reaction of bis-allylic diacetate 1 with the sodium salt of dimethyl malonate ([NaCH(CO 2 Me) 2 ] ϭ NaCHE 2 ) which gives spirocyclopropane 4 via the isolable monoalkylated intermediate (rac)-2 Ϫ Scheme 1. Internal nucleophilic attack in the zwitterionic π-allyl-Pd intermediates exo-3 and endo-3, derived from 2, leads to the spirocyclopropanes endo-4 and exo-4 respectively.It was found (Table 1 in reference [6a] ) that reaction of 1 with NaCHE 2 at room temperature in THF in the presence of 1.5 mol-% (PPh 3 P) 4 Pd gives a 95:5 ratio of isomers of 4 (93% yield). Analogous reaction at 65°C reduced the selectivity and a 60:40 ratio of isomers of 4 is obtained in 75% yield. Buono et al. suggested that the structure of the major product (95%) obtained at room temperature allows the determination of the configuration of the preferred π-allylϪPd intermediate (exo-3 versus endo-3). The identity and structures of spirocyclopropanes exo-4 and endo-4 were 'confirmed by COSY and NOESY NMR experiments'. The major isomer was assigned as endo-4. As evidence, the NOESY spectrum of the 95:5 mixture of isomers of 4 was presented (Figure 1).Two sets of correlations in the NOESY are emphasised by the authors; set i: between signals assigned as norbornene alkenyl protons H 3 ,H 4 (isochronous) and two singlets [7] assigned as the methylene protons H 6 (δ ϭ 3.3) and [a]

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[2+1] Cycloadditions of Terminal Alkynes to Norbornene Derivatives Catalyzed by Palladium Complexes with Phosphinous Acid Ligands

2005

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Secondary phosphine oxides (SPOs) have been widely used for the synthesis of tertiary phosphine oxides and have found applications as Wittig-Horner reagents [1][2] and, later, as effective ligands for transition-metal complexes.[3] Recently, Li et al. showed that SPOs form air-stable palladium complexes, such as POPd1, when they are mixed with PdCl 2 (MeCN) 2 and then treated with Et 3 N.[4] These complexes proved efficient as catalysts in several cross-coupling reactions [4][5] as well as in asymmetric allylic alkylations.[6] Recent reports showed also that these new ligands are suitable for other types of catalyzed reactions such as the hydrolysis of nitriles [7] and the asymmetric hydrogenation of imines [8] and alkenes.[9] Our continued interest in the metal-catalyzed cycloaddition reactions between alkynes and norbornadiene [10] prompted us to investigate the catalytic behavior of palladium(ii) complexes coordinated by SPOs.First, we developed an easier way to synthesize the palladium catalyst 1. Upon treatment of Pd(OAc) 2 with tertbutyl(phenyl)phosphane oxide (L 1), dihydrogen di-macetatotetrakis(tert-butylphenylphosphinito -k -P)dipalladate (1) was quantitatively obtained without further treatment (Scheme 1).[11] Second, as a model we examined the reaction of phenylethyne (3 a) with norbornadiene (2) in the presence of 2.5 mol % of 1 in toluene at 50 8C for 24 h. Unexpectedly, the palladium(ii) complex 1 coordinated by L 1 favored the formation of benzylidenecyclopropane (4 a) as a single diastereomer in 17 % yield (Scheme 2) and contaminated by an unidentified byproduct (5 %). Surprisingly, a similar reaction using the known chloro-bridged analogue 5[6a-12] as catalyst did not work. Furthermore, in the reaction catalyzed by 5, the addition of 10 mol % of AgOAc (4 equiv relative to

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Evidence of Formation of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Carbon Nucleophiles

Cited by 6 publications

References 28 publications

Experimental Evidence on the Existence of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Nucleophiles

Experimental Evidence on the Existence of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate with Stabilized Nucleophiles

On the Evidence for Formation of anexo-π-Allyl Complex Intermediate in the Pd0-Catalyzed Alkylation of a Bicyclic Allylic Diacetate

[2+1] Cycloadditions of Terminal Alkynes to Norbornene Derivatives Catalyzed by Palladium Complexes with Phosphinous Acid Ligands

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