Ethers s.a. Alkoxy

Esterification s. Carboxylic acid esters from carboxylic acids, Redoxesterification Esters, active s. Carboxylic acid esters, active Etherates s. Alane etherates Ethers (s. a. Alkoxy...,... 

Halogenethers (s. a. Alkoxy-halides, Dihalogenethers, Monochloromethyl ether) Halogenethyl. . . s. a. Chloro-ethyl. . . ... 

Reaction of racemic a-alkyl-a-(l H-1,2,4-triazol-l-yl)acetophenones with Grignard reagents in boiling diethyl ether affords exclusively the (RS/S -enantiomeric pairs. On the other hand, reaction of racemic a-alkoxy-x-(17/-l,2,4-triazol-l-yl)acetophenonc with Grignard reagents leads, under chelation control, to the (R/ /5S)-enantiomeric pair82. 

Allylic alcohols from sulfones.1 Polish chemists have extended the Julia synthesis of alkenes (11, 474) to a synthesis of allylic alcohols. In the presence of 1 equiv. of BF3 etherate, a-alkoxy aldehydes react with lithiafed sulfones to form adducts that are converted to allylic alcohols on reduction with sodium amalgam. This reaction was developed specifically for a synthesis of prostaglandins from Corey s lactone-aldehyde, but should have wider application. 

A general procedure for the cycloaddition reactions of a-alkoxy aldehydes with Brassard s diene 7 using Eu(hfc), or magnesium bromide-diethyl ether complex as Lewis acid catalyst is given below. A comparison of substituent effects and catalyst influence is shown in the following table. 

The influence of Lewis acids on the diastereoselectivity of the cycloaddition of /f-alkoxyalde-hydes has also been studied35. Magnesium bromide, highly effective for a-alkoxyaldehydes, fails in the case of the cycloaddition of aldehyde 10 to diene 2 and the reaction does not exhibit any selectivity, probably due to a change of mechanism to Mukaiyama s aldol type. One reason may be the change of solvent from tetrahydrofuran to a mixture of benzene and diethyl ether. The additions of aldehyde 10 to other dienes are more selective but diastereoselectivity is still much lower than for the a-alkoxy aldehydes. Boron trifluoride-diethyl etherate complex also leads to a mixture of four possible products. Excellent selectivity is achieved for the titanium(IV) chloride catalyzed addition of aldehyde 10a to diene 2b, 11c is obtained as the only product. 

Figure 12. Transition temperatures observed on heating 4-n-alkoxy-4 -cyanobiphenyls [228], poly n-[(4 -(4"-cyanophenyl)phenoxy)alkyl]vinyl ether]s ( ) = 17-32, pdi= 1.09- 1.21) [122- 127, 212, 213], n-[(4 -(4"-cya-nophenyl)phenoxy)alkyl]vinyl ethers [122-127] and a-ethoxy-(u-(4-n-alkoxy-4 -cyanobiphenyl)s [122-127] from the glassy ( ), crystalline (O), SmC ( ), SmA ( ) and nematic (A) states.

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