Oxidative scission

The final two stages are very straightforward. Oxidative scission of the C3-C5 double bond in 6 with ozone provides triketone 5 which, without purification, is subjected to a base-induced intramolecular aldol/dehydration reaction. The crystalline product obtained from this two-step sequence (45 % overall yield) was actually an 85 15 mixture of ( )-progesterone and a diastereomeric substance, epimeric at C-17. Two recrystallizations afforded racemic progesterone [( )-(1)] in diastereomerically pure form. 

Scheme 5 details the synthesis of / -cormorsterone (14) from 17. Oxidative scission of both carbon-carbon double bonds in 17 with ozone, followed by two straightforward operations, furnishes intermediate 38. The stability of the oxime in these systems is noteworthy, and is attributed to its hindered nature. At this juncture, it is instructive to note that substituted cyclopentene rings, like the... 

As in the synthesis of (+)-26 (Scheme 8), treatment of (-)-27 with chromic acid accomplishes oxidative scission of the carbon-carbon double bond, and provides (-)-26 after an intramolecular bislactonization reaction (Scheme 16). By analogy to the conversion of 50 into 51 (see Scheme 8), treatment of (-)-26 with ammo-... 

A rather interesting synthesis of the basic ring system based upon oxidative scission of indole precursors was used to prepare prazepam (24), a muscle... 

Note 2 Some main-chain scissions are classified according to the mechanism of the scission process hydrolytic, mechanochemical, thermal, photochemical, or oxidative scission. Others are classified according to their location in the backbone relative to a specific structural feature, for example, a-scission (a scission of the C-C bond alpha to the carbon atom of a photo-excited carbonyl group) and P-scission (a scission of the C-C bond beta to the carbon atom bearing a radical), etc. 

The reaction mechanism was thoroughly studied utilizing 90 as a substrate (85CB4086). Predominantly oxidative scission of the carbocycle occurs... 

Sometimes, TPAP produces the oxidative scission of carbon-carbon bonds in a-hydroxyketones.73... 

In the case of hydroxylated 4-nitrophenol, the two bonds between adjacent -OH groups might undergo easy oxidative scission, but in 2-nitrophenol only one bond of this type is found in hydroxylation. This explains why the photo-Fenton degradation of 2-nitrophenol proceeds at about half the rate of that for 4-nitrophenol. 

Oxidative scission of carbohydrates directly to 3-carbon synthons... 

The di-(cyclohexylidene)-D-mannitol contained a terminal a-glycol group because (a) oxidative scission with lead tetraacetate consumed one mole of the oxidant and gave one mole of formaldehyde, together with an acid-labile derivative of D-arabinose, and (b) its dimethyl ether yielded the known crystalline 5,6-dimethyl-D-mannitol (1,2- is identical) when heated with aqueous acid.1 0 Since graded acidic hydrolysis of the diketal furnished 3,4-cyclohexylidene-D-mannitol,3 it must have possessed the 1,2 3,4-structure and the parent triketal must have been 1,2 3,4 5,6-tri-(cyclohexylidene)-D-mannitol. 

There is abundant information to support the contention that the lower-melting monoisopropylidene-mannitol (m. p. 85°) is the 3,4-derivative. For example, its tetrabenzoate is identical with that obtained by acetonation of 1,2,5,6-tetrabenzoyl-mannitol,11498 the structure of which is based on independent evidence.114 The larger fragment resulting from the oxidative scission of the D-enantiomorph of the isopropylidene-man-nitol with lead tetraacetate is 2,3-isopropylidene-D-//treo-dihydroxy-succinic dialdehyde, characterized by its subsequent conversion into D-i/ireo-tartaric acid.126 When methylated and hydrolyzed, the L-enantio-morph of the monoketal affords a tetramethyl-mannitol, which, in turn, yields dimethyl-L-glyceraldehyde with lead tetraacetate.127 Each of these facts is in itself proof that the acetone residue occupies the 3,4-position in the mannitol molecule. 

When the benzylidenation of sorbitol is carried out under slightly different conditions, a dibenzylidene-D-sorbitol (m. p. 219-221°, after purification via its dibenzoate) is obtained.29 116 Wolfe, Hann and Hudson29 demonstrated that oxidative scission of the diacetal resulted in the consumption of one molecular equivalent of lead tetraacetate and in the production of formaldehyde, together with a dibenzylidene-aldehydo-pentose, which yielded L-xylose when heated with aqueous... 

The mechanistic aspects of LTA oxidation are more complicated and the results indicate several pathways dependent on the steric environment of the glycols. In cases where geometry is favorable, oxidative scission via a cyclic intermediate (11) proceeds by a two-electron transfer (pad) a, Scheme 7). With trans-diols possessing antiperiplanar hydroxy groups, which for steric reasons cannot form the lead(IV) cyclic intermediate (11), an alternative cyclic pathway consisting of an intramolecular proton transfer in... 

In addition to the oxidative scission of 1,2-diols, the reaction can be extended to related 1,2-bifunc-tional compounds such as oxiranes, 1,2-dicarbonyl compounds, 2-hydroxy aldehydes, ketones and acids, a-amino alcohols, 1,2-diamines and also to polyols. LTA cleaves a-hydroxy acids much more readily than do periodates and both reagents oxidize 2-hydroxy aldehydes and 1,2-dicarbonyl compounds relatively slowly. Only periodic acid in water reacts with oxiranes via the corresponding diols. 

The primary formation of o-gluconic acid and o-glucosone simultaneously with o-glucose and o-fructose may be accounted for by two types of oxidative scission of the disaccharide linkage, at a and b. The former leads to D-fructose and... 

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