Ethers from aldehydes

Two techniques have been described for producing trimethylsilyl enol ethers from aldehydes or ketones (10) reaction of (CH2)2SiCl and (C2H3)2N in DMF and reaction of LiN(C2H3)2, which generates enolate ions in the presence of... 

Superior yields of ethers from aldehydes are obtained by the use of several other electrophilic species. The addition of 5 mol% of trityl perchlorate to a mixture of triethylsilane and 3-phenylpropanal in dichloromethane at 0° produces an 83% yield of bis-(3-phenylpropyl) ether within 10 minutes (Eq. 176),329 Reductive polycondensation of isophthalaldehyde occurs with two equivalents of triethylsilane in the presence of 10 mol% of trityl perchlorate to give 40-72% yields of polyether with average molecular weights ranging from 6,500 to 11,400 daltons (Eq. 177).337 Addition of one equivalent of an alkoxytrimethylsilane to the reaction mixture produces unsymmetrical ethers in good to excellent yields. Thus, a mixture of (ii)-cinnamaldehyde, 3-phenylpropoxytrimethylsilane, and triethylsilane in dichloromethane reacts under the influence of a catalytic amount of trityl perchlorate to give the unsymmetrical ether in 88% yield (Eq. 178).329... 

Formation of enol ethers from aldehydes or ketones... 

Acyclic acetals are simple protecting groups for aldehydes and ketones, and we have previously reported their synthesis catalyzed by Bi(OTf)3 [104]. Acyclic acetals can also be converted to other useful functional groups. For example, allylation of acyclic acetals to give homoallyl ethers has been well investigated, and we have reported a Bi(OTf)3-catalyzed method for the same [105]. The success of Bi(OTf)3-catalyzed formation and allylation of acyclic acetals prompted us to develop a one-pot method for the synthesis of homoallyl ethers from aldehydes, catalyzed by bismuth triflate. A one-pot process saves steps by eliminating the need for isolation of the intermediate and thus minimizes waste. Three one-pot procedures for the synthesis of homoallyl ethers were developed [106]. 

Silyl enol ethers from aldehydes 54 and esters 57 are reagents that give clean reaction at the y-position with a variety of electrophiles 58. Acylation occurs under Friedel-Crafts conditions, and the crowded esterifying group (i-Pr)2CH in 59 ensures that reaction occurs entirely at the y-position. The product is a mixture of double bond positional isomers 61 as both are conjugated with one of the carbonyl groups. 

Trimethylsilyl enul ethers. House et al. have described two procedures for the preparation of trimethylsilyl enol ethers from aldehydes and ketones. In one method triethylamine in THF is used as base. These conditions usually afford an equilibrium mixture, and in fact the method is very satisfactory for equilibration. The more highly substituted enol ether usually predominates, as in the example ... 

Although it has been stated that di- and tri-haloketones and a-haloaldehydes (irrespective of the degree of halogen substitution) tend to yield only enol phosphate esters, further qualification of this statement is appropriate. The formation of silyl ethers from aldehydes or ketones and silyl phosphites has already been noted (see section III.A). Reactions between silyl phosphites and trifluoroacetaldehyde or perfluoroacetone and other similar compounds initially lead to silyl ethers of (a-hydroxyalkyl)phosphonic diesters in which all the fluorine is retained, although subsequent change leads to fluorinated enol phosphate esters. Sekine et also observed the formation of (a-silyloxyalkyl)phospho-... 

D. Kataki, P. Phukan, Tetrahedron Lett. 2009, 50, 1958-1960. Iodine-catalyzed one-pot three-component synthesis of homoallyl benzyl ethers from aldehydes. 

In the case of TMEDA, stereoselection in favor of the syn product (98 2) is enhanced over that achieved with Diiso-propylethylamine (94 6). Along with bases sueh as Triethy-lamine and ethylisopropylamine, TMEDA facilitates the preparation of cyanohydrin trimethylsilyl ethers from aldehydes and Cyanotrimethylsilane. It has been suggested that eoordination by nitrogen induces formation of an active hypervalent cyana-tion intermediate from cyanotrimethylsilane. The conjugate addition of thiols to enones has been successfully catalyzed by using TMEDA in methanol at room temperature, as exemplified by the reaction of 10-mercaptoisobomeol and 4-/-butoxycyclopentenone... 

Iron(III) chloride forms numerous addition compounds, especially with organic molecules which contain donor atoms, for example ethers, alcohols, aldehydes, ketones and amines. Anhydrous iron(III) chloride is soluble in, for example, ether, and can be extracted into this solvent from water the extraction is more effective in presence of chloride ion. Of other iron(III) halides, iron(III) bromide and iron(III) iodide decompose rather readily into the +2 halide and halogen. 

The Gattermann-Koch formylatioii was found unsuited to the preparation of aldehydes from phenols and phenol ethers such aldehydes may be obtained by Gatteimann s aldehyde reaction. 

A useful catalyst for asymmetric aldol additions is prepared in situ from mono-0> 2,6-diisopropoxybenzoyl)tartaric acid and BH3 -THF complex in propionitrile solution at 0 C. Aldol reactions of ketone enol silyl ethers with aldehydes were promoted by 20 mol % of this catalyst solution. The relative stereochemistry of the major adducts was assigned as Fischer- /ir o, and predominant /i -face attack of enol ethers at the aldehyde carbonyl carbon atom was found with the (/ ,/ ) nantiomer of the tartaric acid catalyst (K. Furuta, 1991). 

MILLER - SNYDER Aiyl Cyanide Synthesis Synthesis of benzonitnies from aldehydes via oxime ethers Formation of p-cyanophenol from p nrtrobenzaldoxime and p-nitiobenzonitnle (used as a sometimes recyclable chain carrier)... 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

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