Di-tert-butyl phosphine

Pd-Catalyzed Displacement of the Remaining Chloro Atom on C2 by Phenols (Fig. 10).15 To a 10-ml flame-dried Schlenk flask with resin 61 (0.10 mmol, 1.0 equiv.) are added a phenol (0.50 mmol, 5.0 equiv.), Pd2(dba)3 (0.007 mmol, 0.07 equiv.), l,l -biphenyl-2-yl-[di-(tert-butyl)]-phosphine (phosphine ligand) (0.028 mmol, 0.28 equiv.), and K3P04 (0.70 mmol, 7.0 equiv.). The Schlenk flask is purged with Ar and charged with anhydrous toluene (1.0 ml). The reaction is heated to 80° under Ar. 

Besides the nature of anion (X), the type of phosphine ligands also plays a pivotal role. Bulky diphosphines such as (l,3-bis[(di-sec-butyl)phosphino]propane (DsBPP)), l,3-bis[(di-tert-butyl)phosphine] propane (DtBPP), and bis(9-... 

Larger chalcogen-phosphorus heterocycles, although less common in the literature, are accessible via a variety of synthetic routes.2,83,84 For example, the cyclic trimer (SPR)3 (R = 2,4,6-tri-tert-butylphenyl) contains a puckered six-membered P3S3 ring and is produced in the reaction of a phosphinic chloride with lithium sulfide (Equation 73).98 Additionally (R P)3Se5 (R = 2,4-di-tert-butyl-6-wopropoxyphenyl), synthesised from the oxidation of a primary phosphine with three equivalents of elemental selenium (Equation 74), has... 

Vinylsilane to copper transmetallation has entered the literature,93 93a,93b and a system suitable for catalytic asymmetric addition of vinylsilanes to aldehydes was developed (Scheme 24).94 A copper(l) fluoride or alkoxide is necessary to initiate transmetallation, and the work employs a copper(ll) fluoride salt as a pre-catalyst, presumably reduced in situ by excess phosphine ligand. The use of a bis-phosphine was found crucial for reactivity of the vinylcopper species, which ordinarily would not be regarded as good nucleophiles for addition to aldehydes. The highly tailored 5,5 -bis(di(3,5-di-tert-butyl-4-methoxyphenyl)phosphino-4,4 -bis(benzodioxolyl) (DTBM-SEGPHOS) (see Scheme 24) was found to provide the best results, and the use of alkoxysilanes is required. Functional group tolerance has not been adequately addressed, but the method does appear encouraging as a way to activate vinylsilanes for use as nucleophiles. 

This addition proceeds more readily with the more electron rich 2.6-di-tert-butyl-4-methyl-X -phosphorin 109 b or 2,6-dimethyM-phenyl-X -phosphorin 109 c. The H-NMR signals are in accord with the proposed structure (Table 15). The resonance of the phospha-barrelene 110 a m benzene appears at 6 = + 65 ppm (H3PO4 standard) which corresponds to the resonance of tertiary phosphines. 

The BBrs reaction with 1. l-dimethoxy-2.4.6-di-tert-butyl-4-(4 -methoxyphenyl)-X -phosphorin 200 leads to cleavage of both methoxy groups in addition to the methoxy group at the phosphorus, the 4 -methoxy group is attacked. The 2-hydro-4-(4 -hydroxyphenyl)-phosphinic acid methyl ester 201 can be methylated with methyl iodide in methanol/sodium methylate at the phenolic group, leading to 202, which can also be prepared by hydrogen peroxide oxidation of 2.6-di-tert-butyl-4-(4 -methoxy phenyl)-X -phosphorin 204 to 203, followed by diazomethane methylation (see Table 13, p. 61). 

To our knowledge, the first examples of asymmetrically substituted monocyclic phosphoranes are 60 and 61, described by Moriarty et al.135 and involving the reaction of a substituted o-benzoquinone136,137 (Scheme 6) on an aminophosphine (59), itself obtained by alcoholysis of 58 with l-( — )-menthol. In contrast to the amino phosphine 53 (Scheme 5), 59 is a mixture of the diastereoisomers 59a and b, and its reaction with 3,5-di-tert-butyl-l,2-benzoquinone yields two diastereoisomeric phosphoranes, 60a and b. Finally, alcoholysis of the P(V)—NR2 bond138 in 60a and b leads to 61a and b or 62. 

Hamada, Y., Matsuura, F., Oku, M., Hatano, K., and Shioiri, T. Synthesis Mid application of new chiral bidentate phosphine, 2,7-di-tert-butyl-9,9-dimethyl-4,5-bis(methylphenylphosphino)xanthene, Tetrahedron Lett. 1997, 38, 8961-8964. 

Ng JK-P, Chen S, Li Y, Tan G-K, Koh L-L, Leung P-H (2007) Cyclopalladation of the prochiral (di-tert-butyl)(diphenylmethyl)phosphine kinetic lability of the corresponding (-H)-phosphapalladacyclic Pd-C bond and the reluctance of the phosphine to bind in a monodentate fashion. Inorg Chem 46 5100-5109... 

Di-tert-butyl peroxide Phosphinic acid esters... 

C-H Activation. Di-tert-butyl(methyl)phosphine is frequently used as a ligand in palladium-catalyzed Ar-H and Het-H arylation reactions. When the reaction is performed on heterocyclic conpounds, the targeted direct functionalization usually occurs at a position adjacent to a heteroatom. The nature of the ligand can have a dramatic influence on the regioselectivity of the arylation process. Although aryl halides are most commonly used... 

The effect of the halogen of the aryl halide was also carefully studied using bromobenzene and chlorobenzene as the electrophile. When the arylation was performed on ethyl 4-oxazole carboxylate using di-tert-butyl(methyl)phosphine as the Ugand and cesium carbonate as the base, the product of C5 arylation B was obtained when bromobenzene was used as the electrophile. Conversely, the product of C2 arylation A was formed if chlorobenzene was employed (eq 16). Similar results were obtained for the arylation of tert-butyl 4-thiazole carboxylate when mbidium carbonate was used as the base (eq 16). Again, it should be noted that the regioselectivity is highly dependent on the choice of the base and the phosphine. 

Arylation of Quinoline N-Oxides and Pyridines N-Oxides. An efficient protocol to directly arylate quinoline A-oxides was developed using palladium acetate as the catalyst and potassium carbonate as the hase. A survey of different phosphines demonstrated that the sterically less encumbered di-tert-butyl(methyl)phosphonium tetrafluoroborate provides higher yields relative to tri-iert-hutylphosphine. Using this protocol, 15 quinohne A-oxides were arylated in good to excellent yields (eq 1). ... 

A similar protocol for the arylation of isoquinohne A-oxides has been described. A screen of different phosphines showed that di-tert-butyl(methyl)phosphonium tetrafluorohorate provides a greater regioselectivity in favor of the Cl-arylated compound than tricyclohexyl or tri-terf-butylphosphine (eq 2). 

Applications of these C-H activation processes in polymerization reactions have also been reported in the literature. For example, a palladium-catalyzed C-H arylation polycondensation was carried out between a thiophene unsubstituted at the 2- and 5- positions and its 2,5-dibromo derivative. The transformation was effected in the presence of palladium acetate, a phosphine, and cesium carbonate in DMF at 100 °C for 48 h (eq 23). A survey of different phosphines showed that similar yields, molecular weights (Mn), and polydispersity indexes (PDI) could be obtained using di-tert-butyl(methyl)phosphonium tetrafluoroborate or tri-cyclohexylphosphonium tetrafluoroborate as the ligand. ... 

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