Ethers by oxidants

Presumably, compound 115 has also been isolated, as an extremely volatile liquid, in 15% yield from a complex mixture of other bicyclic ethers by oxidation of 1,6-hexanediol (118) with lead tetraacetate198,199 (see Scheme... 

Later on, all the protecting groups will be removed the silyl groups with fluoride and the p-methoxybenzyl ether by oxidation with Ce(IV). In Ley s recently completed synthesis9 of azadirachtin 64 after 22 years of hard labour the key intermediate was 65. You will notice benzyl ethers, acetals and a silyl ether. This is a more modem, one might almost say minimalist, use of protection. In an ideal world no protecting groups would be necessary but in a real synthesis they will almost certainly be required as we shall see in the rest of the book. But our aim should be to keep them to a minimum. 

Copper compounds are catalysts for the Michael addition reaction (249), olefin dimerizations (245, 248), the polymerization of propylene sulfide (142), and the preparation of straight-chain poly phenol ethers by oxidation of 2,6-dimethylphenol in the presence of ethyl- or phenyl-copper (209a). Pentafluorophenylcopper tetramer is an intriguing catalyst for the rearrangement of highly strained polycyclic molecules (116). The copper compound promotes the cleavage of different bonds in 1,2,2-tri-methylbicyclo[1.1.0]butane compared to ruthenium or rhodium complexes. Methylcopper also catalyzes the decomposition of tetramethyllead in alcohol solution (78, 81). 

Pentanediol is often superior to other diols such as 2,3-butanediol for these reactions because of higher distereoselectivities in reactions with nucleophiles and the more facile cleavage of the resulting hydroxy ether by oxidation-p-elimination. Removal of the chiral auxiliary is usually carried out with Pyri-dinium Chlorochromate oxidation followed by p-elimination using KOH, K2CO3, piperidinium acetate, dibenzylammonium trifluoroacetate, " or DBU. In some cases, 1,3-butanediol is preferred because the final 3-elimination may be effected under milder conditions. ... 

Allylpalladium(II) complexes are also formed by reaction of a Pd(0) precursor with allyl formates or carbonates. [Pd(PCy3)2] reacts with allylaryl ethers by oxidative addition of the C—O bond , and with A-allyltriethylammonium bromide by C—N bond cleavage ... 

The above transformations led Sugasawa 14) to assign the hydroxyl in ring A to C-1 and therefore songorine may be represented by XXVII. Since reduction of songorine with LiAlH4 affords napelline 8), the latter is the ring C equatorial alcohol XXVIII. In order to be able to form a carbinolamine ether by oxidation of the C-1 hydroxyl, models show that... 

Degradation of aldehydes is accomplished via their silyl enol ethers by oxidative cleavage with hydrogen peroxide in a two-phase system with added PTC. ... 

Owing to its inactivity there is no very satisfactory chemical method for the determination of ether either alone or in mixtures, and the usual methods of examination are concerned with the impurities present. Attempts to determine ether by oxidation with acid dichromate present so many possible errors that the method seems to be valueless. It is, however, interesting to note that the ether content in ether-air mixtures has been successfully determined with a considerable degree of accuracy by a modified Pregl micro-method of ultimate combustion (Coste and Chaplin ). The standard Pregl combustion apparatus was modified as follows ... 

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