Silver alkoxides

Macomber, R. S. et al., Synth. React. Inorg. Met.-Org. Chem., 1977, 7, 111-122 The dried solid product from interaction of lithium phenoxide and silver perchlorate in benzene (probably largely silver phenoxide) exploded on gentle heating. Other silver alkoxide derivatives were unstable. 

Alkyl hahdes in the presence of silver oxide react with alkyl malates to yield alkoxy derivatives of succinic acid, eg, 2-ethoxysuccinic acid, H00CCH2CH(0C2H )C00H (12,13). A synthetic approach to produce ethers of malic acid is the reaction of malic esters and sodium alkoxides which affords 2-alkoxysuccinic esters (14). 

A number of compounds of the types RBiY2 or R2BiY, where Y is an anionic group other than halogen, have been prepared by the reaction of a dihalo- or halobismuthine with a lithium, sodium, potassium, ammonium, silver, or lead alkoxide (120,121), amide (122,123), a2ide (124,125), carboxylate (121,126), cyanide (125,127), dithiocarbamate (128,129), mercaptide (130,131), nitrate (108), phenoxide (120), selenocyanate (125), silanolate (132), thiocyanate (125,127), or xanthate (133). Dialkyl- and diaryUialobismuthines can also be readily converted to secondary bismuthides by treatment with an alkali metal (50,105,134) ... 

A useful variation of the Williamson synthesis involves silver oxide, Ag20, as a mild base rather than NaH. Under these conditions, the free alcohol reacts directly with alkyl halide, so there is no need to preform the metal alkoxide intermediate. Sugars react particularly well glucose, for example, reacts with excess iodomethane in the presence of Ag20 to generate a pentaether in 85% yield. 

A useful application of the silver-mediated additions is 1,3 -diene synthesis by three-carbon elongation of aldehydes [48,51,53]. The bimetallic reagent 3-trimethylsilyl-l-propenylzirco-nocene chloride (A Scheme 8.23) reacts with aldehydes under the influence of a catalytic amount of Ag+ to give the intermediate zirconocene-alkoxide B, which then undergoes a Peterson-type 1,4-elimination of TMS alkoxide to stereoselectively afford ( )-dienes (fc/Z > 96 4) (Scheme 8.23). A Wittig reaction yields the same products without stereoselectivity (ca. 1 1 mixtures of E- and Z-isomers). 

The five-membered ring can also be formed by intramolecular nucleophilic attack of an alkoxide on a carbamate such as for the formation of 196 from 195 <1997T9553>, by dehydration of fV-carbamate-pipecolic acid derivatives <2002EJO3936>, by treatment of amino-amides under Eschweiler-Clarke conditions <1999TA3371>, or by treatment of hydroxyl aminonitriles with silver trifluoroacetate <2002JA2951> (Scheme 57). 

As esters the alkyl halides are hydrolysed by alkalis to alcohols and salts of halogen acids. They are converted by nascent hydrogen into hydrocarbons, by ammonia into amines, by alkoxides into ethers, by alkali hydrogen sulphides into mercaptans, by potassium cyanide into nitriles, and by sodium acetate into acetic esters. (Formulate these reactions.) The alkyl halides are practically insoluble in water but are, on the other hand, miscible with organic solvents. As a consequence of the great affinity of iodine for silver, the alkyl iodides are almost instantaneously decomposed by aqueous-alcoholic silver nitrate solution, and so yield silver iodide and alcohol. The important method of Ziesel for the quantitative determination of alkyl groups combined in the form of ethers, depends on this property (cf. p. 80). 

The 6,7-dihydro-5/f -1,4-dioxepin (266) has been prepared (54CR(38)982). and more recently it has been shown that the 2,3-dihydro-5jF/-l,4-dioxepins (263) and (265) can be produced from 1,4-dioxine-halocarbene adducts (264), either by heating under reflux in xylene or by treatment with bases. The allylic chlorine atom in (263) is readily substituted by alkoxide or cyanide ions (77ZC331, 76UKZ968). Saturated rings of type (267) have been prepared by the treatment of cyclic acetals of ethane-1,2-diol with vinyl ethers in the presence of boron trifluoride, and l,4-dioxepan-5-one (268) has been prepared by the reaction of bromoform and silver nitrate with aqueous dioxane (60AG415). 

Reaction of [Mo(NO)(Me2pzb)I(OR)] with silver acetate in the presence of the alcohol ROH leads to the bis(alkoxides) [Mo(NO)(Me2pzb)(OR)2]. The mixed alkoxides were similarly prepared.126 The structures of several dialkoxides (Et, Pr Pr , Pr Et, Et) have been investigated in detail in view of the rather bulky character of the ligands at molybdenum. 

Ethers For the synthesis of ether, the Williamson ether synthesis is considered as the best method. It involves the SN2 reaction between a metal alkoxide and a primary alkyl halide or tosylate. The alkoxide needed for the reaction is obtained by treating an alcohol with a strong base like sodium hydride. An alternative procedure is to treat the alcohol directly with the alkyl halide in the presence of silver oxide, thus avoiding the need to prepare the alkoxide beforehand. 

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