Triphenylphosphine ether formation

The triphenylphosphine-azodi formate ester combination is a strong dehydrating system in the alkylation of imines by alcohols (103) and the formation of aryl alkyl ethers (104). The synthesis of isonitriles (105) from for-mamides can be formulated according to the following interactions. 

The successful implementation of this strategy is shown in Scheme 4. In the central double cyclization step, the combined action of palladium(n) acetate (10 mol %), triphenylphosphine (20 mol %), and silver carbonate (2 equiv.) on trienyl iodide 16 in refluxing THF results in the formation of tricycle 20 (ca. 83 % yield). Compound 20 is the only product formed in this spectacular transformation. It is noteworthy that the stereochemical course of the initial insertion (see 17—>18) is guided by an equatorially disposed /-butyldimethylsilyl ether at C-6 in a transition state having a preferred eclipsed orientation of the C-Pd a bond and the exocyclic double bond (see 17). Insertion of the trisubstituted cycloheptene double bond into the C-Pd bond in 18 then gives a new organopal-... 

The addition of more than one molar equivalent of triphenylphosphine to a solution of PPN S N or Ph As S N in acetonitrile causes an immediate color change from deep blue to orange due to the formation of the SjN" anion 465 nm), which can be isolated in ca. 50 % yield by addition of diethyl ether to the solution... 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

The reaction of bis-phenylpropargyl ether (321) with tris(triphenylphosphine)rhodium chloride in benzene or toluene led to the formation of the unusual organometallic compound (322), which can be viewed as a derivative of an oxygen-rhodium pentalene system. Reaction of the rhodium complex (322) with sulfur leads to the corresponding 4,6-diphenyl-l,3-dihydro[3,4-c]furan (323). The selenium and tellurium analogs (324) and (325) were made in a similar manner (Scheme 111) (76LA1448). 

Dehydration of diols to cyclic ethers. The reagent dehydrates a variety of diols to cyclic ethers with formation of triphenylphosphine oxide as the co-product. Yields of cyclic ethers are high from 1,2-, 1,4- and 1,5-diols. Although (Z)-2-butene-1,4-diol is converted into 2,5-dihydrofuran in 95% yield, the (E)-isomer is converted in 35-40% yield into 3,4-epoxy-l-butene.1... 

The formation of the pentacoordinate species (XX) is also supported by the reaction of the triphenylphosphine derivative (XXI) with CO in methanol to give, besides allyl methyl ether, methyl butenoate (14). 

In 1980 Trost and Keinan reported on allylic alkylations of tin enolates such as 33 catalyzed by tetrakis(triphenylphosphine)palladium (equation 12). The stannyl ethers led to a rapid and clean monoaUcylation with high regioselectivity. Thereby, alkylation generally occurred at the less substituted end of the allyl moiety with formation... 

The catalytic activity of various zeolites in the Claisen rearrangement was investigated. It was found that H-mordenite and HB catalyse the rearrangement of allyl phenyl ether to 2-allylphenol and the cyclisation of latter compovmd to 2-methyldihydrobenzofuran. The reaction was accompanied by the formation of dimers and oligomers, which could be suppressed by triphenylphosphine treatment of the catalysts. This treatment led in the case of HB to better selectivities to the major reaction products. 

H-mordenite and HB are able to catalyse the Claisen rearrangement of allyl phenyl ether. The reaction is accompanied by the cyclisation of the initial rearrangement product and other acid catalysed side reactions. A drawback is the formation of dimers and oligomers, but improvement with respect to these undesired side reactions can be achieved by deactivation of the outer surface of the zeolite with triphenylphosphine in the case of H13. 

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