Carboxylic cleavage, thermal

A non-biomimetic synthesis of /J-(-)-horsfiline (57) has also been recently reported which was based on a thermal intermolecular 1,3-dipolar cycloaddition reaction as outlined in Scheme 7 [63J. The reaction of the optically active menthyl ester 67 acting as a dipolarophile, with the JV-methylazomethine ylide 68 (thermally generated in situ from sarcosine and formaldehyde) proceeded with n-facial diastereoselectivity to produce a chromatographically separable mixture of 69 and the unwanted diastereomer. Subsequent cleavage of the chiral auxiliary, followed by removal of the carboxylic acid group by the Barton radical method provided J7-(-)-horsfiline. 

This species, completely characterized also by X-ray diffraction studies as its tetrahexylammonium salt (Figure 1)5 was responsible for the epoxidation of a series of structurally diversified olefins with typical selectivities of ca. 95% and chemical yields in the range 85-95%. These catalysts have found industrial applications in the epoxidation of alkenes and in the oxidative cleavage of alkenes to carboxylic acids. The favourable characteristics of these catalysts are thermal stability, ease of synthesis, stability to oxidation, solubility- in both water and organic solvents, effectiveness as phase transfer catalysts. 

The reaction of (148) with glycol and hydrogen peroxide gave (149). Compound (19b) has been reduced with liAlH4 to the corresponding alcohol, which was converted into the aldehyde and bromomethyl and aminomethyl derivatives that are of pharmaceutical interest. A mild method for the hydrolysis and decarboxylation of various amides of methyl 3-aminothiophen-2-carboxylates has been developed. Thermal decomposition of (150) led to cleavage of the thiophen ring, with extrusion of sulphur and formation of the isothiazole (151). ... 

Heteratisine esters undergo a facile thermally induced ring cleavage which has unusual features (154). Thus, pyrolysis of the acetate (CCCXCVI) or the benzoate (CCCXCVII) proceeds with elimination of 1 mole of the respective carboxylic acid to give pyroheteratisine (CDXV) [Amax 238 m/x (e 10,600)] in about 90% yield and isopyroheteratisine... 

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