Periodate olefin cleavage

The periodate olefin cleavage generated large amounts of colloidal MnO2 waste and sodium iodate (NalOj). The process therefore involved multiple unit operations and suffered from poor volume productivity and oxidation efficiency (three out of four available oxygens in NalO4 are wasted). 

Figure 14.3 Process flow chart for periodate olefin cleavage to obtain 39.

Similarly to oxidative olefin cleavage with periodate, the first intermediate formed is ester 35, here a perruthenate at the oxidation level +VI1 A -elimination releases ketone 6 and the mthenium(V) acid 36 /V-Methylmorpholine-N-oxide (NMO) serves in this case to regenerate the perruthenate(VII) speck s, and must therefore be introduced in stoichiometric quantity. 

Use of the chiral carbon pool for cyclopentenone preparation is also known. The fungal metabolite terrein [88] was selectively monoacetylated and then reduced with chromous chloride to enone [89]. Acetylation and olefin cleavage with ruthenium tetroxide aiwi sodium periodate led to aldehyde [90], which was readily decarbonylated to [65] (51). An alternative route (52) began with the less common S,S-tartaric acid [91], converted in four steps to diiodide [92]. Dialkylation of methyl methylthiomethyl sulfoxide with [92] gave the cyclopentane derivative [93]. Treatment of [93]... 

Without added sodium periodate, olefins are converted only into ctT-diols by OSO4 upon workup, therefore, it is plausible that sodium periodate further oxidizes osmium species and triggers the cleavage of carbon-carbon bond, as shown here. 

Oxidative cleavage of the olefin is accomplished by the method of ijemieux-Johnson.12 The process begins with dihydroxylation of the double bond using osmium tetroxide (see Chapter 3)T leading to a cis diol and osmium(VI) oxide. The added periodate has two functions first, it reoxidizes the osmium(VI) species to os-mium(VIII), but it also cleaves the glycol oxidatively to an aldehyde. This is the reason for utilizing several equivalents of periodate. The periodate is in turn reduced from the +VH to the +V oxidation state. 

Overhand, Overkleeft and their collaborators have synthesised a variety of SAAs [39]. The synthesis of Fmoc-protected 6 ( Fig. 2) is illustrated in Scheme 2 [15]. Tri-O-acetyl-D-glu-cal was converted into the SAA precursor 43 in five steps. Formation of the trichloroacetimi-date derivative 44 and a subsequent Overman rearrangement was used to introduce the amino group onto the pyran scaffold giving 45. Hydrogenation of the olefin in 45 was accompanied by cleavage of the silyl ether to afford the primary alcohol which was oxidised with a catalytic amount of ruthenium (III) chloride in the presence of sodium periodate giving 46. Subjection... 

Masamune has also completed a synthesis of tylonide hemiacetal (291) based on the creative use of enantioselective aldol condensations, as shown in Scheme 2.26. The aldol condensation of 328, derived from (/f)-hexahydromandelic acid and prop anal, was found to be >100 1 diastereoselective, affording the 2,3 syn compound 329 in 97% yield. Transformation to the p,7-unsaturated ester 330 occurred via selenoxide elimination and periodate cleavage followed by esterification. Formation of the silyl ether, reduction, and protection of the ester followed by ozonolysis of the terminal olefin gave the diol-protected aldehyde 331. The C-11 to C-15 segment 332 was then completed via chain elongation and a subsequent reduction-oxidation sequence in 34% overall yield from 330. 

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