My PhD dissertation - Institut Fresnel

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4 However, the mechanism proposed and the results reported thus far could also be explained by a concerted mechanism in which the second equivalent of hydroxide ion and the cleavage and protonation of the alkyl residue would happen simultaneously. This alternative mechanistic possibility will be displayed in more details in the general part and discussed in view to the results obtained. In view to the sequence suggested by L. Hey and C.K. Ingold, two hydroxide ions and one phosphonium cation should be involved during or prior the rate limiting step of the reaction. [ , ] To verify this statement L. Horner and H. Hoffmann 31 32 [ , ] and W.E. McEwen et al. 33 34 respectively studied the kinetic of decomposition for several p-substituted-phenyltriphenylphosphonium halides and p-substituted-benzyltribenzyl phosphonium halides. The results obtained by both research groups confirmed that the reaction follows a third order kinetic, with a first order dependence on the concentration of phosphonium and a second order dependence on the concentration of hydroxide ions. Furthermore, L. Horner and H. Hoffmann [31] provided theoretical arguments to rationalize this mechanism. Phosphorus, as an element of the second period of the Mendeleev Table, is able to exceed the octet rule and form pentacovalent species. The ionic phosphonium hydroxide should thus exist in equilibrium with its corresponding hydroxyphosphorane intermediate. The latter, being a weak acid, also coexists with its conjugated oxidophosphorane base. Finally the formation of a stabilizing pπ-dπ phosphorus-oxygen bond constitutes a driving force for the elimination of an alkyl anion. Although this SN(P) mechanism is commonly accepted and accounts for experimental results reported so far, [ ] C.A. Vander Werf et al. 35 proposed two conceivable variations of that mechanism: the second attack of hydroxide and the departure of the anion could be synchronous or the first step could involve the formation of an unstable intermediate with two hydroxide ions bound to phosphorus. In addition to the mechanism they proposed, L. Hey and C.K. Ingold [29] observed that if the phosphonium salt was bearing different type of substituents, the relative ease of P-C bond cleavage in the pentacovalent intermediate was following the anionic stability of the expelled group. Later, many research groups oriented their efforts towards stereochemistry investigations and studied enantiomerically pure cyclic [ - ] 36 38 [35, , and linear 39 40] phosphonium halides, where phosphorus constituted the sole stereogenic center. The phosphine oxides obtained by treatment of these salts under alkaline conditions revealed that the reaction occurred stereospecifically with complete inversion of configuration at phosphorus. Various suggestions [35, 37, 38] have been proposed to explain this stereochemistry. The most plausible [35] rationalization of this experimental result was the formation of a trigonal-bipyramidal transition state were the leaving group and the hydroxide both occupy apical positions. R 1 P R3 R4 R2 K HO I HO R 4 R 1 P + KI R 3 R 2 K HO H 2O O R 4 R 1 P + H 2O R 3 R 2 H 2O R 1 P R3R4 + R2H O
5 However, this mechanism suffers from inconsistencies since some cyclic substrates were found to show partial racemization or complete retention of stereochemistry at phosphorus [ , ] 41 42 . These results could be explained by ring strain. Phosphetanium (four- membered ring) and phospholanium (five-membered ring) salts preferentially adopt, in the trigonal bipyramidal intermediates, an equatorial-apical relation (90 °) due to angle constraint. Since apical positions are assumed to be favored for the departing group and the hydroxide [ 43 ] [ 44 ] , a Berry pseudorotation must mediate the move of the more stabilized anion to the apical position. The latter pseudorotation thus accounted for the partial retention of configuration at phosphorus center. In summary, even if applicable to non cyclic cases, this general explanation of the observed stereochemistry for the alkaline decomposition of phosphonium salts does not illustrate the whole scheme of this process. 1.3 Objectives of this Work Organometallic techniques, particularly the halogen/metal permutation proved to be the method of choice in many areas of organic synthesis [ , ] 45 46 , have [ ] 47 . This is especially remarkable when it comes to organophosphorus chemistry and the preparation of tertiary phosphine ligands. Thus, phosphorus will constitute a leitmotiv in the present thesis work, and several aspects of its chemistry and applications will be taken into account. Up to now, the principal method for the preparation of tertiary phosphines was the treatment of phosphorus trichloride with the appropriate organometallic reagent (organomagnesium or organolithium) [ ] 48 . The present research work will first focus on the preparation of tertiary phosphines via a modification of the above mentioned synthetic route. The use of trialkyl phosphites [ - ] 49 51 instead of phosphorus trichloride, already reported in few instances, was believed to provide several advantages and allow large scale preparation of different tertiary phosphines from simple and known to more elaborate ones. R'= P(OR) 3 N O R'M (M = Mg, Li) O O OH O O PR' 3 N Ph
Page 1: Various Facets of Organophosphorus
Page 5: III Remerciements Je tiens à remer
Page 9: 3.3.6 Relevance of the Data Assesse
Page 13: VII Literature References 115 Compo
Page 17: IX Version Abrégée Les composés
Page 21 and 22: 1 Introduction 1 The present thesis
Page 23: 3 research groups in the field are
Page 27: 7 At first, a double bromine/lithiu
Page 30 and 31: 10 Although the most frequently emp
Page 32 and 33: 12 The preparation of the latter ph
Page 34 and 35: protected to its dioxolane derivati
Page 36 and 37: N (S)-14 1) NBS, THF, - 75 °C 2) -
Page 39 and 40: 3 Alkaline Decomposition of Phospho
Page 41 and 42: 3.2 Alkyl Carbanions Stabilities in
Page 43 and 44: 3.3.1 Mechanistic Discussion on the
Page 45 and 46: 25 The assumption reported by these
Page 47 and 48: 27 However, in the eventuality of a
Page 49 and 50: 29 To prepare tertiary phosphines b
Page 51 and 52: 31 Table 4. Mixed tertiary alkylpho
Page 53 and 54: 33 were comparable to those obtaine
Page 55 and 56: 35 led to the formation of di-tert-
Page 57 and 58: 37 depending on the alkyl substitue
Page 59 and 60: 39 4 A Novel Access to Atropisomeri
Page 61 and 62: 41 Since the homocoupling of the ha
Page 63 and 64: 43 Few other attempts to selectivel
Page 65 and 66: 45 The second phenol ether 36 was f
Page 67 and 68: 47 The enantiomeric purity was chec
Page 69 and 70: 49 A second purpose of this derivat
Page 71 and 72: 51 substrates considered. In conseq
Page 73 and 74: 53 Single-crystal X-ray analysis of
Page 75 and 76:
55 To convert atropisomer Ia into I
Page 77 and 78:
57 This finally allows one to use t
Page 79 and 80:
the steric bulk and charge delocali
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61 To check the reproducibility of
Page 83:
63 Figure 9. Full lineshape analysi
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66 suitably substituted dilithiobip
Page 89:
Experimental Part
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70 deuterochloroform (CDCl3) unless
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72 1 H NMR: δ = 7.32 (dddd, J = 9,
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1 H NMR: δ = 6.96 (s, 3 H), 6.94 (
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76 C21H21O9P (448.36) calcd. C 56.2
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78 C12H12BrN (250.13) calcd. C 57.6
Page 102 and 103:
80 C13H13NO2 (215.25) calcd. C 72.5
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82 3.1.1 Dialkyl-N,N-diethylaminoph
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84 apparatus. The solution was adde
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86 Di-tert-butylisopropylphosphine
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88 13 C NMR: δ = 32.9 (d, J = 12 H
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90 13 C NMR: δ = 41.5 (d, J = 61 H
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31 P NMR: δ = 53.4 ppm. 92 C16H31O
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94 13 C NMR: δ = 40.8 (d, J = 3 Hz
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96 31 P NMR settings: It is known t
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98 Theoretical ratio: (96.1:3.9) Ex
Page 123 and 124:
101 4 The Preparation and Racemate
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103 extraction protocol with ethyl
Page 127 and 128:
105 extracted with ethyl acetate (2
Page 129 and 130:
107 (+)-(M)-Dimethyl-6,6’-dibromo
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109 (+)-(M)-2,2’-Dibromo-6,6’-b
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111 1 H NMR: δ = 7.2 (m, 20 H), 7.
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113 2,2’-Dilithio-6,6’-bis(meth
Page 137:
References
Page 140 and 141:
116 Conference Proceedings, Naples,
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118 [ 70] J. Drowart, C.E. Myers, R
Page 144 and 145:
120 [117] S.T. Graul, R.R. Squires,
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122 [170] B.H. Lipshutz, F. Kayser,
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124 [212] M. Schlosser, in Organome
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O P 27i: p. 30, 80 C 9H 21OP P 26b:
Page 156:
P P P O 2: p. 11, 59 3 P O O O 11:
Page 160:
Nom Maurin Prénom Michaël 129 Cur
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My PhD dissertation - Institut Fresnel

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