Diol Cleavage

Scheme 2.20 The simultaneous application of an oxidant and reductant for 1,2-diol cleavage.

With a particular poly(vinyl alcohol) sample no periodic acid is consumed, within the limits of analytical aecuracy. This indicates no apparent (1,2-diol) cleavage. However, the viscosity average molecular weight of the sample decreased from 250,000 to 100,0(X), Explain these results in terms of the structures of po y(vinyl acetate) and polyfvinyl alcohol). [The analytical technique is described by P. J. Flory and F. S, Leutner, J. Polym. Set. 3,880 (1948) 5, 267(1950).]... 

CLEAVAGE OF C-C BONDS. DECARBOXYLATION, BAEYER-VILLIGER OXIDATION, AND 1,2-DIOL CLEAVAGE IN A TOTAL SYNTHESIS... 

Oxidative Cleavage Reactions. Among the numerous methods for 1,2-diol cleavage there exist only a few that involve catalytic ruthenium reagents, for example Ruthenium(III) Chloride with Sodium Periodate Attempted selective monooxidation of a 1,2-diol to the hydroxy aldehyde with catalytic TPAP and NMO resulted in carbon-carbon bond cleavage to provide the aldehyde (eq 11). Furthermore, attempted oxidation of an anomeric a-hydroxy ester failed instead, in this case decarboxy-lation/decarbonylation and formation of the lactone was observed (eq 12). However, Dimethyl Sulfoxide-Acetic Anhydride provided the required a-dicarbonyl unit. Retro-aldol fragmentations can also be a problem. ... 

The DMP oxidation of 1,2-diols generally cleaves the glycol C—C bond, as illustrated by the synthesis of tricyclic enol ether 883 from diol 882 via tandem 1,2-diol cleavage-intramolecular cycloaddition (Scheme 3.355) [1220]. 

Alcohols (diols, polyols, sugan) Lead(IV) acetate -dichloro fluorescein Diol cleavage of vicinal diols, e. g. sugars, sugar alcohols. The lead tetraacetate consumed is no longer available to decompose the fluorescent dichlorofluorescein. [3, 8]... 

In the noble metal-catalyzed oxidations described above vicinal diol cleavage is sometimes observed as a side-reaction but never as a main reaction. Oxidative diol cleavage usually involves stoichiometric oxidants such as periodate (Malaprade oxidation) and there is a great need for catalytic procedures employing inexpensive, clean oxidants such as O2 or H2O2. 

The chemical viability of the L-dopa diol cleavage process involved in the generation of the acromelic acid C-4 substituents has been examined in a biomimetic sense by Baldwin s group in syntheses of stizolobic acid 16,22 3-(6-carboxy-2-oxo-4-pyridyl)alanine 17,22 and stizolobinic acid 1523 (Figure 5). 

These results lend strong support to the L-dopa diol cleavage proposal for the biosynthesis of acromelic acid C-4 pyridone moieties. 

An asymmetric synthesis of aminocyclopentitols 134-137 has been used in the synthesis of trehazolin via free-radical cycloisomerization of enantiomerically pure, alkyne-tethered oxime ethers derived from D-mannose (Scheme 17).84 Treatment of 2,3 5,6-di-(9-isopropylidene-D-mannofuranose (128)85 with ethynylmagnesium bromide gave compound 129, which underwent sequential one-pot acid hydrolysis plus diol cleavage to give 130, oximation of which afforded the radical precursor 131, in 41% overall yield from 129. The free hydroxyl group of 131 was protected as acetate 132 and tert-butyldimethylsilyl ether 133, which were isolated as inseparable... 

Make models of the cis and trans diols. Notice that it is much easier to form a five-membered cyclic periodate from the cis diol A than from the trans diol B. The cis periodate intermediate is of lower energy than the trans periodate intermediate because of the lack of strain in the cis periodate ring. Because any factor that lowers the energy of a transition state or intermediate also lowers AG and increases the rate of reaction, diol cleavage should proceed more slowly for trans diols than for cis diols. 

Scheme 68. Alternative rationale for the formation of emycins D (251) and G (254) 1,3-diol cleavage of emycin H analog 288...

The unsaturated ester function in furanosyl imidazoles 754 can be converted into the corresponding aldehyde 755 either through ozonolysis or dihydroxylation/diol cleavage (Scheme 185) <1999JOC7158>. 

EtsN in CH2CI2 in the presence of 4-dimethylaminopyridine (Scheme 13.68). Dihydroxylations of the trimethylsilyl ethers of 217 and 218 generate the 4-amino-4-deoxy-heptono-1,4-lactam derivatives 219 and 220, respectively [121]. Lactam hydrolysis of 219 with LiOH, followed by the Malaprade diol cleavage with NaI04 and further oxidation and deprotection, allows the preparation of 4- p/-polyoxamic acid [122]. Lactam 217 and its enantiomer derived from (5 )-24 have been converted into all four stereomers of cw-l,2-dihydroxypyrrolizidine [123]. Compounds 217 and 218 have been used also to prepare the rm/i5 -2,3-c/5 -3,4-dihydroxyprolines [124,125]. 

This is readily done by isopropylidene removal, diol cleavage, and formation of the anomeric p-nitrobenzoate 315. Axial introduction of the allenyl moiety yields stereoselectively, as predicted, the a-C-manno derivative 316 after chair inversion. Degradation of the allenyl group to... 

Diols are oxidatively cleaved by reaction with periodic acid (HIO4) to yield carbonyl compounds, a reaction similar to the KMnO cleavage of aJkenes just discussed. The sequence of (1) alkene hydroxylation with OsO< j followed by (2) diol cleavage with HIO4 is often an excellent alternative to direct alkene cleavage with ozone or potassium permanganate. 

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