Hydroxy acids Ethers

The lac resin is associated with two lac dyes, lac wax and an odiferous substance, and these materials may be present to a variable extent in shellac. The resin itself appears to be a polycondensate of aldehydic and hydroxy acids either as lactides or inter-esters. The resin constituents can be placed into two groups, an ether-soluble fraction (25% of the total) with an acid value of 100 and molecular weight of about 550, and an insoluble fraction with an acid value of 55 and a molecular weight of about 2000. 

One of the more complex local anthetics in fact comprises a basic ether of a bicyclic heterocyclic molecule. Condensation of 1-nitropentane with acid aldehyde, 79, affords the phthalide, 81, no doubt via the hydroxy acid, 80. Reduction of the nitro group... 

Increasing interest is expressed in diastereoselective addition of organometallic reagents to the ON bond of chiral imines or their derivatives, as well as chiral catalyst-facilitated enantioselective addition of nucleophiles to pro-chiral imines.98 The imines frequently selected for investigation include N-masked imines such as oxime ethers, sulfenimines, and /V-trimcthylsilylimines (150-153). A variety of chiral modifiers, including chiral boron compounds, chiral diols, chiral hydroxy acids, A-sull onyl amino acids, and /V-sulfonyl amido alcohols 141-149, have been evaluated for their efficiency in enantioselective allylboration reactions.680... 

In this case, the aluminium salt of the hydroxy acid is soluble in the reaction medium. It precipitates on addition of a number of solvents such as alcohols or ethers. 90% product-selectivity was observed in preparative syntheses (up to 40 g of pure 2-(6-methoxynaphthyl)propionic acid per run). The power consumption was given as about 2.7 kWhkg-1. 

The obvious disconnection in cyclopeptide alkaloids and indeed the strategy employed in most total syntheses of this type of compound is the formation of the aryl ether bond. Many groups chose to form the macrocyclic aryl ether by S Ar reaction. We decided to follow the inverse strategy, i.e., displacement of an allylic leaving group by a phenolate. In case of the natural cyclopeptide alkaloids, this would involve activation of yS-hydroxy-a-amino acids, which is likely to be accompanied by extensive elimination. Elimination is not possible when a-methylene- -hydroxy acids are used. Additionally, the double bond activates the leaving group and provides a handle for a possible later side chain attachment. 

Amides of keto acids were reduced to amides of hydroxy acids biochemically using Saccharomyces cerevisiae to give optically pure products [7059]. Refluxing with lithium aluminum hydride in ether for 6 hours reduced both the ketonic and the amidic carbonyl in A -methyl-5-phenyl-5-oxopentanamide and gave 82% yield of 5-methylamino-l-phenylpentanol [1134]. 

The synthesis of (-t-)-benzoylselenopederic acid (569) (477) (Scheme 71), the left-hand half of pederin (147), began with (-f-)-3-keto imide 570, which was subjected to the recently developed syn-directing Zn(BH4)2 reduction (482) to give 5yn-a-methyl-3-hydroxy acid derivative 571. Imide 571, after protection of the hydroxyl group as the THP ether, was reduced with DIBAH, and the resulting aldehyde was treated with lithium enolate of tm-butyl acetate to give the p-... 

For this selective addition, the best catalyst precursors were Ru(methallyl)2(dppe) 1 and Ru(methallyl)2(dppb) 2. The choice of the appropriate complex depended on the steric demand of both the alkyne and the carboxylic acid. A large variety of carboxylic acids and alkynes have been used, including N-protected amino acids, a-hydroxy acids, and functionalized alkynes such as enynes, diynes and propargylic ethers [21-23] (Scheme 10.4). The addition took place under mild conditions and carboxylic adds of... 

The type of products formed in reactions of /(-hydroxy acids with sulfur tetrafluoride depends on the substituents on the carbon alom adjacent to the hydroxy group. Acids such as 3-hy-droxypropanoic acid (21) and 3-hydroxybutanoic acid (22) give, in addition to 1,1,1,3-tetra-fluoroalkanes, mainly dimeric products, i.e. fluorinated esters or ethers, together with small amounts of unsaturated acid fluorides. In contrast, n7C -4,4,4-trifluoro-3-hydroxybutanoic acid (23), depending on the reaction conditions, affords 3,3,3-trifluoro-l-(lrifluoromethyl)propyl fluorosulfite or a mixture of 1,1,1.2,4,4,4-hcptafluorobutanc and l,l,1.4.4,4-hcxafluorobut-2-ene.116... 

In general, dehydration means loss of water molecules from chemical substances, irrespective of their structure. Even if all cases where water is bonded in hydrate form are excluded, a number of reactions remain which also include formation of nitriles from amides, lactones from hydroxy acids etc. However, the present treatment will concentrate on the heterogeneous catalytic decomposition of alcohols in the vapour phase, which can be either olefin-forming or ether-forming reactions, and on the related dehydration of ethers to olefins. 

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