Sulfoxide complexes alkylation

The patent literature contains several references to the use of sulfoxide complexes, usually generated in situ, as catalyst precursors in oligomerization and polymerization reactions. Thus, a system based upon bis(acrylonitrile)nickel(0> with added Me2SO or EtgSO is an effective cyclotrimerization catalyst for the conversion of butadiene to cyclo-1,5,-9-dodecatriene (44). A similar system based on titanium has also been reported (407). Nickel(II) sulfoxide complexes, again generated in situ, have been patented as catalyst precursors for the dimerization of pro-pene (151) and the higher olefins (152) in the presence of added alkyl aluminum compounds. 

This chapter reports principally on studies with ruthenium chiral phosphine and chiral sulfoxide complexes and their use for catalytic hydrogenation. We have used the familiar diop ligand, [2R,3R-(—)-2,3-Oisopropylidene-2,3-dihydroxy-l,4-bis(diphenylphosphino) butane] (7) a related chiral chelating sulfoxide ligand dios, the bis(methyl sulfinyl)butane analog (21) (S,R S,S)-(+)-2-meth-ylbutyl methyl sulfoxide(MBMSO), chiral in the alkyl group and R-(+)-methyl para-tolyl sulfoxide(MPTSO), chiral at sulfur. Preliminary data on some corresponding Rh(I) complexes are presented also. 

Toda, F., Tanaka, K., and Okuda, T. (1995) Optical Resolution of Methyl Phenyl and Benzyl Methyl Sulfoxides and Alkyl Phenylsulfinates by Complexation with Chiral Host Compounds Derived from Tartaric Acid, J. Chem. Soc., Chem. Commun., 639-640. 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

In this year, White et al. [113] reported highly effective synthesis of tricyclic lactone structure, which is a common structure of class I galbulimima alkaloids, through tandem allylic C-H activative alkylation/Diels-Alder reaction cascade of a-allylated y-butenolide 167 (Scheme 67). In the presence of Pd(II) bis(sulfoxide) complex, the reaction of 167 with active methane compoxmd 168 initially gave triene 169. Under the present conditions, 169 smoothly cyclized to give tricyclic lactone 170 as a mixture of endo/exo adducts in 75% yield. 

Colona and coworkers oxidized a variety of alkyl aryl and heterocyclic sulfides to the sulfoxides using t-butyl hydroperoxide and a catalytic amount of a complex (97) derived from a transition metal and the imines of L-amino acids. Of the metals (M = TiO, Mo02, VO, Cu, Co, Fe), titanium gave the highest e.e. (21%), but molybdenum was the most efficient catalyst. The sulfoxides were accompanied by considerable sulfone125. 

Structural Identification of a Palladium Complex with a Chiral Sulfoxide Ligand Used in Asymmetric Palladium-Catalyzed Allylic Alkylations... 

Valentine and Curtis (1975) extended the synthetic utility of potassium peroxide by reporting the successful solubilization of K02 in dry dimethyl sulfoxide using dicyclohexyl- 18-crown-6 ([20] + [21]). Corey et al. (1975) used 18-crown-6 to solubilize KOz in dimethylformamide, dimethoxyethane and diethyl ether, whilst Johnson and Nidy (1975) reported its solubilization in benzene. A wide variety of chemical transformations have been realized with K02 complexes of crown ethers. With alkyl halides the main reaction products are peroxides, alcohols and olefins (Johnson and Nidy, 1975). Peroxides are... 

A different approach to the resolution of sulfoxides was recently reported by MikcJajczyk and Drabowicz (35). It takes advantage of the fact that sulfoxides as well as other sulfinyl compounds ry easily form inclusion complexes with 3-cyclodextrin. Since -cycl dextrin (the host) is chiral, its inclusion complexes with racemic guest substances are mixtures of diastereomeis that can be formed in unequal amounts. In this way a series of alkyl phenyl, alkyl p-tolyl, and alkyl benzyl sulfoxides has been resolved. However, the optical... 

The stereospecific conversion of sulfinates into sulfoxides of known chirality has been applied as a general method for determining the absolute configuration of a wide range of optically active sulfinic esters. For example, the absolute configurations of a series of alkyl alkanesulfinates obtained by asymmetric synthesis (107) or resolution via 3-cyclodextrin inclusion complexes (106) were determined by this method. 

The oxidation of alkyl aryl sulfides to sulfoxides with oxochromium(V) complexes is first order in oxidant and in substrate. The better correlation of log k with a+ rather than a and the low magnitude of p+ value (-1.19) were interpreted as evidence for a rate-determining single-electron-transfer mechanism. This was further supported by good correlation in the plots of log k versus oxidation potential/ionization energy. 

Rhodium(II) forms a dimeric complex with a lantern structure composed of four bridging hgands and two axial binding sites. Traditionally rhodium catalysts faU into three main categories the carboxylates, the perfluorinated carboxylates, and the carboxamides. Of these, the two main bridging frameworks are the carboxylate 10 and carboxamide 11 structures. Despite the similarity in the bridging moiety, the reactivity of the perfluorinated carboxylates is demonstrably different from that of the alkyl or even aryl carboxylates. Sohd-phase crystal structures usually have the axial positions of the catalyst occupied by an electron donor, such as an alcohol, ether, amine, or sulfoxide. By far the most widely used rhodium] 11) catalyst is rhodium(II) acetate [Rh2(OAc)4], but almost every variety of rhodium] 11) catalyst is commercially available. 

Sulfides are generally oxidized much faster than alkenes, and in the presence of excess oxidant further oxidation to the sulfone occurs. In the cases where the reaction is conducted in an asymmetric way, the chiral catalytic system may react faster with one enantiomeric sulfoxide to form the sulfone than with the other, so that kinetic resolution of the primarily formed sulfoxide may occur. In general, the reaction is carried out with alkyl hydroperoxides like TBHP in the presence of a metal catalyst like Mo, W, Ti or V complexes. In some cases the sulfoxidation with hydroperoxides can take place without the need of a metal catalyst. Both examples will be discussed in the following. 

In combination with H2O2 (salen)Mn(III) complexes 173a, b, i-n have also been employed by Jacobsen and coworkers as catalysts for the asymmetric oxidation of sulfides to sulfoxides, without a need for additives. From the structurally and electronically different Mn-salen catalysts screened, 173i turned out to be the most active and selective one (equation 58) . While dialkyl sulfides underwenf uncafalyzed oxidation with H2O2, aryl alkyl sulfides were oxidized only slowly compared wifh fhe cafalyzed pathway. Using... 

Recently, Feng and co-workers reported an asymmetric sulfide oxidation" catalyzed by titanium complexes bearing HydrOx ligands, for example, 576 (Scheme 8.199). ° Enantioselectivities approached a level of synthetic utility for oxidation of aryl alkyl sulfides 632 although the yields of the sulfoxide 633 were poor due to overoxidation to the sulfone 634. The overoxidation is especially significant for reactions with high enantioselectivity. 

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