Diols to lactones

Chiral Alcohols and Lactones. HLAT) has been widely used for stereoselective oxidations of a variety of prochiral diols to lactones on a preparative scale. In most cases pro-(3) hydroxyl is oxidized irrespective of the substituents. The method is apphcable among others to tit-1,2-bis(hydroxymethyl) derivatives of cyclopropane, cyclobutane, cyclohexane, and cyclohexene. Resulting y-lactones are isolated in 68—90% yields and of 100% (164,165). 

Nakata showed that stoich. RuOyCCl oxidised steroidal diols to the corresponding ketones [237] electrogenerated RuO from RuO /aq. NaCl/Na(H3PO ) pH 4/ Pt electrodes converted diols to lactones and keto acids (Tables 2.1-2.4) [267] and RuCyaq. 10(0H)3/CC1 -CH3CN oxidised 3-(benzyloxy)-l,2-octanediol to the acid (Tables 3.4, 3.5) [107]. A diol was converted to a lactone by stoicheio-metric oxidation with RuOyCCl as part of the total synthesis of the quassinoid ( )-amarolide [82],... 

The system RuCl3/Na(Br03)/aq. M Na COj [213] converted diols to acids while TPAP/NMO/PMS/CH3CN oxidised diols to lactones [119] TPAP/NMO/PMS/ CH3CI2 was used for diol to dione conversion for sensitive steroidal alcohols [503]. The reagent TPAP/NMO/PMS/CH Cl oxidised primary-secondary 1,4- and 1,5-diols to lactones (Fig. 2.19) [481]. 

Typical examples are listed in Table 2.1. A few oxidations are effected by RuO but in general it is too powerful an oxidant for this purpose. The system RuCyaq. NaCl-CCy Pt anode oxidised benzyl alcohol to benzaldehyde and benzoic acid and p-anisaldehyde to p-anisic acid [24], and a wide range of primary alcohols and aldehydes were converted to carboxylic acids, secondary alcohols to ketones, l, -diols to lactones and keto acids from RuOj/aq. NaCl pH 4/Na(H3PO )/Pt electrodes (Tables 2.1-2.4). The system [RuO ] "/aq. K3(S303)/Adogen /CH3Cl3 oxidised benzyhc alcohols to aldehydes [30]. The oxidation catalyst TPAP (( Pr N)[RuO ]) (cf. 1.3.4) is extremely useful as an oxidant of primary alcohols to aldehydes and secondary alcohols to ketones without... 

See also page 1650, Section 14, for diols to lactones and page 1652, Section 15 for amino alcohols to... 

Dehydrogenation of 1,4- or 1,5-diols to lactones. This Ru-catalyzed transfer dehydrogenation can be effected with high selectivity when the 2-position of 1 is... 

Heterogeneous oxidation of diols to lactones.1 A mixture of KMn04 and Cu-S04-5H20 is recommended for heterogeneous oxidation of 1,4- and 1,5-diols to lactones. This oxidation can be highly selective since primary alcohols are oxidized... 

Reagent mixtures which utilize a catalytic metal complex, usually with a cooxidant (analogous to the Pt/02 reagent) for the selective oxidation of diols to lactones have been studied recently, with some interesting results. 

A thorough study of the use of HLADH for the enantioselective oxidation of mefo-diols to lactones has provided a venatile and synthetically useful route to enantiomerically enriched lactones. There are two major advantages of this system in that it appears to accept a ftdr amount of structural variatitm and full experimental details are available for preparative scale oxidatitms. A selection of results obtained with this enzyme system is presented in Scheme 14. 

Aliphatic alcohols are converted to a symme-RCOOCH2R) by oxidation with PCC on aluminum without solvent. Oxone in aqueous methanol also converts aryl aldehydes to the corresponding ester. Ally lie alcohols are converted to conjugated esters with Mn02, NaCN in methanol-acetic acid. Primary alcohols are oxidized to the methyl ester with tri-chloroisocyanuric acid in methanol. This reagent also converts diols to lactones. 

Trichloromelamine (TCM), because of the simple procedure, mild conditions, high selectivity, and low cost, is a useful reagent for the selective oxidation of alcohols to the corresponding carbonyl compounds. Oxidation of diols to lactones with two equivalents of TCM in dichloromethane is also reported. Lactones of five- and six-membered rings only were obtained in 87% and 95% yield respectively four- and seven-membered ring lactonization did not occur (Scheme 80) <93JOC5003>. 

Lactones. A-Haloamides, including NCS, oxidize diols to lactones at room .emperature. However,the scope of this reaction has to be established further. 

Selective Oxidations. The selective oxidation of 1,4 and 1,5 primary-secondary diols to lactones is a valuable application of this reagent. Few general mild reagents for the chemoselec-tive oxidation to the hydroxy aldehyde are available. The most widely known reagents are Pt and O2, and Dihydridotetrakis-(triphenylphosphine)ruthenium(II) Hydroxy aldehydes, in their lactol form, are then oxidized further to lactones. The use of TPAP is advantageous in that it is commercially available, employs mild catalytic reaction conditions, and reacts with high selectivity in unsymmetrical cases (eq 8). Lactones have also heen formed from primary-tertiary diols. ... 

Zhao J, Hartwig JF. (2005). Acceptorless, neat, ruthenium-catalyzed dehydrogenative cycliza-tion of diols to lactones. Organometallics, 24, 2441-2446. 

The reaction can be applied to the synthesis of lactone from l,primary-primary diols bearing bulky substituents are oxidized at the sterically hindered position, although the chemoselectivity is modest (Scheme 18). It is noteworthy that the regioselectivity of the Ru-catalyzed reaction of unsymmehical primary-primary diols to lactones is opposite to the Pd-catalyzed reaction. ... 

A review of oxidations using Ag2C03 on celite includes useful sections on the oxidations of lactols and diols to lactones. 

General Synthesis.— The catalyst RuH2(PPh)4 brings about the oxidative condensation of diols to lactones, in addition to the conversion of alcohols to esters. o>-Benzyloxymethyl esters are converted into lactones in 71—91% yield when treated with the hydride abstractor Ph3C BF4 or the radical cation (p-BrPh)3NSbCl6 (Scheme 59). ... 

Use of silver carbonate on Celite (I ) to oxidize primary 1,4-, 1,5-, and 1,6-diols and primary-tertiary diols to lactones, e.g. ... 

Scheme 6.38 Oxidation of aliphatic diols to lactones in water.

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