Pyridinium chlorochromate, oxidation with

What product would you obtain by reduction of digitoxigenin (Problem 27.39) with LiAl.H4 By oxidation with pyridinium chlorochromate ... 

The pyranocoumarin 105 can be prepared via a three-component Diels-Alder reaction between 4-hydroxycoumarin, ethyl vinyl ether and an a-dicarbonyl compound. Similarly to the above, upon treatment of 105 with sulfuric acid in THF, hydrolysis and rearrangement occur to give the furofurochromenone 106. The hemiacetal functionality in 106 may then be oxidized with pyridinium chlorochromate (PCC) to give the lactone 107 <2001EJ03711> (Scheme 28). 

A novel one-pot tandem oxidation-cyclization-oxidation process was successfully applied in the transformation of unsaturated alcohols 250 [Eq. (5.315)].860 The intermediate aldehyde formed by oxidation with pyridinium chlorochromate (PCC) undergoes a carbonyl-ene cyclization followed by an additional oxidation to form 3-substituted piperidinones. 

The secondary alcohol is readily oxidized with pyridinium chlorochromate (PCC)25 (65) which is commercially available or easily prepared by addition of pyridine to a solution of chromium(VI)-oxide in hydrochloric acid. 

Step 2 Oxidation with pyridinium chlorochromate (PCC) affords the aldehyde. Step 3 Wittig reaction provides the TM. (Note The ylide reagent is prepared by treating Ph3P with CD3I to obtain Ph3P+CD3 r and followed by deprotonation with w-BuLi.)... 

Further processing of 57 towards the ketone 60 is readily effected by highly regioselective tosylation of the primary hydroxyl group (66), hydride reduction 58 -> 59, and oxidation with pyridinium chlorochromate (PCC) on aluminum oxide to afford 60 in a yield of 70 % over the three steps (63). Due to the now practical accessibility of these furanoid building blocks supplementary modifications, that have already been performed, become preparatively relevant, e. g. the conversion of tosylate 58 into the 5,6-epoxide (66), C-extensions (63, 66), shortening of the carbon chain via periodation of 57 (63), and transformation of the respective products into acyclic derivatives by acid hydrolysis of the 1,2-0-isopropylidene group (63, 66). 

The reducing power of diborane has been blunted by forming its adduct with dimethyl sulfide. This adduct, Me2S BH3, is stable and commercially available and therefore more attractive as a hydride reagent than diborane itselfNevertheless, the adduct still reduces carboxylic acids to alcohols which are isolated as cyclic boroxins (2 Scheme 1). In a one-pot reaction, carboxylic acids can be reduced to boroxins and then oxidized with pyridinium chlorochromate to the required aldehyde (Scheme I)."... 

OXIDATION WITH PYRIDINIUM CHLOROCHROMATE ADSORBED ON ALUMINA... 

Alkylation of isovaleramide with 1,3-dichlorobut-2-ene yields (139) after methyl-ation acid-catalysed hydrolysis and internal aldol condensation gives ( )-piperitone. The value of piperitenone and isopiperitenone formation, probably via electrocyclic reaction of the pyrolytic acetic acid-elimination product from A - and A -isomers of (49), cannot be assessed in the absence of reaction yields. (S)-(-)-Pulegone is obtained in good yield from (- )-citronellol by oxidation with pyridinium chlorochromate followed by double-bond isomerization. Low-temperature reduction of ( —)-carvone to ( —)-cz5-carveol (140) and... 

Oxidations with pyridinium chlorochromate PCC and pyridinium dichromate PDC. 4 Oxidations with PCC and PDC of secondary hydroxyl groups of sugars and nucleosides is slow and incomplete. The reaction is markedly catalyzed by 3 A molecular sieves. Celite, alumina, and silica are not effective. CH2C12 is the most satisfactory solvent oxidations are slower in C1CH2CH2C1 and C6H5. The rate of oxidation increases in the order 5A<10A<4A<3 A. 

The diastereomeric excess could be increased to > 99.5% by employing the bulky chiral auxiliary (3S,55)-2,6-dimethylheptane-3,5-diol which prevents the solvent effect by suppressing the formation of substrate - reagent - solvent complex. The 2,6-dimethylheptane-3,5-diol moiety was readily removed by oxidation with pyridinium chlorochromate followed by treatment with potassium carbonate in methanol to give the bridged cyclopropanol compound. An example is the cyclopropanation of 56 to give predominantly 57 with > 95% de 57 was converted to (15,65 )-bicyclo[4.1.0]heptan-l-ol. ... 

If the reaction takes place via an anion or in a S 2 fashion, high yields of the product alkyl-cyclopropanes have been obtained. Thus, reaction of methyl 4,6-( -benzyIidene-2,3-dideoxy-2,3-C-[(7 )-(chloromethyl)ethylidene]-a-D-mannopyranoside (1) with lithium aluminum hydride in refluxing tetrahydrofuran gave methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-C-isopropylidene-a-D-mannopyranoside (2) in 89% yield. Similarly, treatment of chloromethylcyclopropane 3 with lithium triethylborohydride, followed by oxidation with pyridinium chlorochromate,. gave ishwarone (4) in 75% yield. ... 

However, this sequence can be reversed. - Thus, the activated cyclopropane can be de-protonated by lithium diisopropylamide, reacted with an appropriate ketone and opened by various methods such as treatment with acid or desilylation with fluoride. Using this reaction sequence, y-lactones 52 with various substituents can be obtained by the intramolecular attack of the ketone oxygen on the siloxy-substituted carbon followed by oxidation with pyridinium chlorochromate. The cyclic hemiacetal intermediates 53 can be converted to the tetrahyd-rofuran derivatives 55 by deoxygenation with triethylsilane/boron trifluoride. 

A serious drawback to this system is that the auxiliary can only be removed under destruction, namely by oxidation with pyridinium chlorochromate, followed by base-induced elimination. The optical purity of ( + )-(15,65)-bicyclo[4.1.0]heptan-l-ol obtained by this sequence was not reported70. 

Synthesis from o-glucose Total syntheses of (-l-)-valyldetoxinine (14) and (—)-detoxin Di (7) were achieved from diacetone D-glucose (Schemes 1 and 2). ° The diacetone D-glucose was oxidized with pyridinium chlorochromate and the resulting ketone... 

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