Ethers to lactones

For the mild C-H oxyfunctionalisation of cyclic steroidal ethers by RuCyaq. Na(IO )/EtOAc-MeCN cf Fig. 4.3, 4.1.4 [86]. 

---

No systematic study of the minimal required amount of lead tetraacetate has been made. In cases where the product of the hypoiodite reaction is an iodo ether (20-hydroxy steroids) the reaction can be interrupted at the iodohydrin stage by reducing the amount of iodine to about 0.5 mole. For the oxidation of iodo ethers to lactones, chromium trioxide-sulfuric acid in acetone has been used. Silver chromate is often added to the reaction mixture but comparable yields are obtained without the addition of silver salt. 

Oxidation of cyclic ethers to lactones (1, 988). A systematic study of this reaction has been reported. In general, yields are good to excellent by either stoichiometric or catalytic procedures. No anhydrides from further oxidation are detected. The oxidation is chemoselective. Oxidation of a secondary position takes precedence over oxidation of a tertiary site. Primary positions are attacked in preference to secondary positions in the oxidation of acyclic ethers.1... 

ZnIMnO,), effects several known oxidations such as oxidation of alkynes to a-diketones, cyclic ethers to lactones, and cycloalkanones to dicarboxylic acids. The paper reports one novel transformation Oxidation of a cyclohexcne to a ketol in moderate yield (36%), equation (1). 

Transition metal catalyzed ring expansions of cyclic ethers to lactones under pressures of CO [51, 52] have been reported for tetrahydrofuran [53], oxetanes, and epoxides [54—56]. Carbonylation of epoxides is particularly important since P-lactone products are challenging synthetic targets (see Section 2.2.5). Using Co(CO)4 in combination with a Lewis acidic Al-salen counterion, the reaction of (R)-propylene oxide and CO occurs with stereochemical retention (Scheme 2.23) [57]. The mechanism is believed to involve Lewis acid activation of the epoxide followed by nucleophilic ring opening with Co(CO)4 [58]. 

BBr is a very useful reagent for cleaving ethers, esters, lactones, acetals, and glycosidic bonds it is used to deoxygenate sulfoxides and in the preparation of image-providing materials for photography (5). 

Figure 3.11 shows the relative reactivity as a function of ring size for two other intramolecular displacement reactions, namely, conversion of ethers from ca-bromoalkyl monoethers of 1,2-dihydroxyben-zene. 

The enol lactone (12.7 g) is added to 157 ml of 0.5 M perbenzoic acid in benzene and allowed to stand at 25° for 140 hr. The solution is cooled to 15° and 15% sodium bisulfite solution is added to neutralize the excess peracid. The organic layer is separated and washed with saturated sodium bicarbonate solution and water. The benzene solution is dried over anhydrous sodium sulfate, filtered and concentrated to 30 ml. The product is crystallized by adding 80 ml of petroleum ether, filtered and washed with petroleum ether to yield 12.8 g (98%) of 3a,20,23-trihydroxy-16a-methyl-17(20)-oxido-ll-oxo-21-norchol-22-enoic acid-24(20)-lactone 3,23-diacetate mp 225-227°. 

Ethers in which at least one group is primary alkyl can be oxidized to the corresponding carboxylic esters in high yields with ruthenium tetroxide. Molecular oxygen with a binuclear copper (II) complex " or PdCVCuCVCO " also converts ethers to esters. Cyclic ethers give lactones. " The reaction, a special case of 19-14,... 

The dimerization of the parent ketene gives the P-lactone. One molecule of ketene reacts across the C=C bond as a donor and the other molecule reacts across the C=0 bond as an acceptor. This is similar to the concerted [2+2] cycloaddition reaction between bis(trifluoromethyl)ketene and ethyl vinyl ether to afford the oxetane (Scheme 26) [127], A lone pair on the carbonyl oxygen in the ketene molecule as a donor activates the C=C bond as the alkoxy group in vinyl ether. 

Additions of silylated ketene acetals to lactones such as valerolactone in the presence of triphenylmethyl perchlorate in combination with either allyltrimethylsilane 82, trimethylsilyl cyanide 18, or triethylsilane 84b, to afford substituted cyclic ethers in high yields have already been discussed in Section 4.8. Aldehydes or ketones such as cyclohexanone condense in a modified Sakurai-cyclization with the silylated homoallylic alcohol 640 in the presence of TMSOTf 20, via 641, to give unsaturated cyclic spiro ethers 642 and HMDSO 7, whereas the 0,0-diethyllactone acetal 643 gives, with 640, the spiroacetal 644 and ethoxytrimethylsilane 13b [176-181]... 

The oxidation of both linear and cyclic ethers to the corresponding acids and lactones by aqueous H202 as catalyzed by TS-1 and TS-2 was reported by Sasidharan et al. (241) (Scheme 17 and Table XXXV). The titanosilicates exhibited significantly better activity (about 55% conversion) and selectivity (98%) than chromium silicates, although vanadium silicates totally failed to catalyze the reaction. Such conversions are usually accomplished using either stoichiometric amounts of chromium trioxide, lead tetraacetate, or ruthenium tetroxide as oxidants (242) or catalytic amounts of Ru04 in the presence of... 

Mn207 also effects oxidation at -45° of a-methylene groups of ethers to give lactones or esters.1... 

The products are ds-fused. They are hydrolyzed by TsOH in aqueous THF to lactols, which can be oxidized by Fetizon s reagent to lactones or converted to dials by DBU. The enol ether group of the adduct can be selectively oxidized by Cl-QH4CO3H or OsO to provide bicyclic tetrahydrofurans. 

Intramolecular [4+2]-cycloaddition reactions, which involve base-induced isomerization of a propargyl ether to an allenyl ether, have been extensively studied. Treatment of 157 with a base caused an intramolecular Diels-Alder reaction of the intermediate allenyl ether to give tricyclic compounds 158 [131]. An asymmetric synthesis of benzofuran lactone 159 was achieved by an analogous procedure [132],... 

Halogens are frequently used as oxidation agents and, under two-phase conditions, they can either be employed as ammonium complex halide salts [3], or in the molecular state with or without an added quaternary ammonium catalyst [4]. Stoichiometric amounts of tetra-n-butylammonium tribromide under pH controlled conditions oxidize primary alcohols and low-molecular-weight alkyl ethers to esters, a,cyclic ethers produce lactones [3], and secondary alcohols yield ketones. Benzoins are oxidized to the corresponding benzils (80-90%) by the tribromide salts in acetonitrile in the presence of benzoyl peroxide [5]. 

Soil. Metabolites of endosulfan identified in seven soils were endosulfan diol, endosulfanhydroxy ether, endosulfan lactone, and endosulfan sulfate (Martens, 1977 Dreher and Podratzki, 1988). These compounds, including endosulfan ether, were also reported as metabolites identified in aquatic systems (Day, 1991). In soils under aerobic conditions, p-endosulfan is converted to P-endosulfan alcohol and p-endosulfan ether (Perscheid et al., 1973). Endosulfan sulfate was the major biodegradation product in soils under aerobic, anaerobic, and flooded conditions (Martens, 1977). In flooded soils, endolactone was detected only once whereas endodiol and endohydroxy ether were identified in all soils under these conditions. Under anaerobic conditions, endodiol formed in low amounts in two soils (Martens, 1977). Indigenous microorganisms obtained from a sandy loam degraded p-endosulfan to endosulfan diol. This diol was converted to endosulfan a-hydroxy ether and trace amounts of endosulfan ether and both were degraded to endosulfan lactone (Miles and Moy, 1979). 

Reductive detelluration of aryldichlorotellurolactones (general procedure) f To a solution of the dichloroteUurolactone (1 mmol) in deoxygenated toluene, (10 mL), under reflux and N2, is added dropwise BujSuH (4 mmol). The reaction is monitored by TLC. After 4 h the solvent is evaporated and the residue chromatographed on Si02 (eluted first with petroleum ether to remove Te and Sn by-products, and then with petroleum ether/EtOAc, 1 5), giving the tellurium-free lactone. 

Renaud and co-workers used 78 for the synthesis of (-)-phaseolinic acid (6) and (-)-pertusarinic acid (8) (Scheme 12) [32, 33]. Radical addition of dimethyl phenylselenomalonate to 78 proceeded with rearrangement of the bicyclics to yield the seleno-acetal 79 [34]. After reductive deselenylation and Baeyer-Villiger oxidation treatment of 80 with BU4NI and BBr3 led to a simultaneous cleavage of the ether, the lactone, and the methyl ester func-... 

---