1.2- Diols manganese dioxide

Hydroxyandrosta-4,6-dien-3-one. A suspension of 42 g of crude androsta-4,6-diene-3j ,17j -diol in 2000 ml of chloroform is treated with 250 g of activated, manganese dioxide. The mixture is then shaken vigorously for 15 min in a stoppered flask. The mixture is filtered and the manganese dioxide washed well with chloroform in order to elute material which initially remains adsorbed on the solid phase. The filtrate is concentrated to a pale yellow, crystalline residue. Recrystallization from acetonitrile gives 38 g (90%) of 17/ -hydroxyandrosta-4,6-dien-3-one as plates mp 211-214°. 

Kubota and co-workers also prepared several 1,2-diols (61) and noted that these substances give the enediones (59) in much better yields than the diosphenols (58). This is consistent with a mechanism which requires, as the first step, hydroxylation of the -double bond of (58) by manganese dioxide followed by oxidation to the intermediate trione. 

Several total syntheses of antirhine (11) and 18,19-dihydroantirhine (14) have been developed during the last decade. Wenkert et al. (136) employed a facile route to ( )-18,19-dihydroantirhine, using lactone 196 as a key building block. Base-catalyzed condensation of methyl 4-methylnicotinate (193) with methyl oxalate, followed by hydrolysis, oxidative decarboxylation with alkaline hydrogen peroxide, and final esterification, resulted in methyl 4-(methoxycar-bonylmethyl)nicotinate (194). Condensation of 194 with acetaldehyde and subsequent reduction afforded nicotinic ester derivative 195, which was reduced with lithium aluminum hydride, and the diol product obtained was oxidized with manganese dioxide to yield the desired lactone 196. Alkylation of 196 with tryptophyl bromide (197) resulted in a pyridinium salt whose catalytic reduction... 

A procedure for the transformation of (+)-tazettine (397) to (+)-pretazettine (395) has been developed (212). The reaction of 397 with LiAlH4 provided a mixture of the diols 536 and 537 in an approximately 9 2 ratio. Thus, it is again apparent that the preferred stereochemical pathway for the delivery of hydride to the neopentyl carbonyl function is from the endo face of the cis-3a-arylhydroin-dole whenever the angular aryl group possesses an ortho substituent. Oxidation of 537 with manganese dioxide gave a mixture (approximately 3 2 1) of (+)-pretazettine (395), (+)-3-epimacronine (400), and (+)-tazettine (397). In a sim-... 

This reagent can be of value not only for its inherent chemoselectivity, but also because of the mild conditions under which oxidation occurs. For example the cyclohexylideneacetaldehydes (2) can be produced by manganese dioxide oxidation of the allylic alcohols despite the instability of (2) to air, acids and bases. Manganese dioxide is known to cleave 1,2-diols, and can cause oxidative rearrangement to... 

The selective oxidation of diols in which one or both hydroxy groups are allylic has been reported on a number of occasions. Reagents which have proved use for this include silver carbonate on Celite, barium manganate/ and manganese dioxide, as illustrated in equations (29)-(31). 

Oxidation of 4,4-dimethyl-l,7-diphenyl-l,6-hcptadiyne-3,5-diol (1) with active manganese dioxide (German firm of Merck) ... 

Two oxidants essentially dominate these oxidations lead tetraacetate in organic solvents and periodic acid in aqueous media. On occasion, other oxidation reagents cause the cleavage of vicinal diols ceric ammonium nitrate [424], sodium bismuthate [482, 483], chromium trioxide [482, 555], potassium dichromate with perchloric acid [949], manganese dioxide [817], and trivalent [779, 789] or pentavalent [798] iodine compounds. 

When tazettinol and isotazettinol were reduced with lithium aluminum hydride and the resultant diols were treated with acid, the ethers, deoxytazettinol (CLIII) and deoxyisotazettinol (CLIV), respectively, were formed. Both deoxytazettinols gave deoxytazettinone (CLV) with manganese dioxide. 

To our mind, the enolate of 19 should exhibit a decided kinetic bias for kinetically controlled protonation on its a face because of the steric encumbrance associated with p proton delivery. In actual fact, rapid introduction of its lithium salt into a 1 4 mixture of water and tetrahydrofuran at -78 °C resulted in its quantitative conversion to 20 (Scheme III). Once the MOM groups had been removed, controlled oxidation with manganese dioxide led to 21, a very pivotal intermediate. To arrive at magellaninone (2), 21 was treated with methyllithium and the resulting unprotected diol 22 was directly reduced with lithium aluminum hydride. Subsequent Jones oxidation proceeded with the customary allylic rearrangement. 

For example, oxidation of the allylic alcohol 33 gave the a, -unsaturated aldehyde 34, used in a synthesis of the macrolactone bafilomycin Ai (6.30). Chemose-lective oxidation of allylic or benzylic alcohols can be achieved in the presence of aliphatic alcohols. Thus, in a synthesis of the alkaloid galanthamine, treatment of the diol 35 with manganese dioxide promoted selective oxidation of the benzylic alcohol to give the aldehyde 36 (6.31). 

Selective oxidation of the benzylic alcohol of the diol 6 to give the ketol 7 is possible by using the oxidant manganese dioxide in a neutral solvent such as acetone at room temperature. Alternatively, silver carbonate on celite heated in a solvent such as acetone or benzene is effective (see Section 6.2). 

Manganese dioxide/potassium hydroxide Carboxylic acids from alcohols Preferential oxidation Lactols from diols... 

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