Alkoxy acids, cleavage preparation

Directed lithiations of alkoxy furans have potential in the synthesis of butenolides, and the tetramethyldiamidophosphate moiety has been successfully used to prepare 3-substituted furans (22). Acidic cleavage of the phosphorus residue then allows access to the corresponding 2-substituted butenolide (23), and the overall process becomes equivalent to using the anion (24) (Scheme 8). 

Benzhydrylamines are better suited than benzylamines as acid-labile linkers for amines. The MBHA linker ( methylbenzhydrylamine ), which is usually used to prepare peptide amides (see Section 3.3), can also be used as a linker for amines (Entry 1, Table 3.21). Hydrogen fluoride is, however, required as the cleavage reagent. Easier to cleave are alkoxy-substituted benzhydrylamines (Entries 2-5, Table 3.21), which can be prepared from the corresponding benzhydryl chlorides [263] or by reductive alkylation [410] or solvolysis [411] of the Rink amide linker. In the case of benzhydrylamines linked to polystyrene as benzyl ethers, treatment with TFA can lead to the release of the linker into solution (acidolysis of the benzylic C-O bond, see Figure 3.18). 

It was reported [39] that osmium tetroxide promoted catalytic oxidative cleavage of ds-stilbene and other olefins. The ds-stilbene catalytic oxidative cleavage gave benzoic acid in 95% yield. The process for the preparation of substituted aromatic and heteroaromatic aldehydes and carboxylic acids by the oxidation of substituted stilbenes has been patented [40]. Stilbenes of various substituents (Ri, R2 = H, Cl-4 alkyl, Cl-4 alkoxy, OH, NO2, CN, COjH, CONH2, SO3H, halogen X = C, N Z = CHO, CO2H ... 

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