Ether formation From alkene

Acidic clays are widely applied in the dehydration of alcohols [38]. Although similar to zeolites in their capacity to induce the formation of both alkenes and ethers, selective alkene synthesis is possible. Various layered materials (clays, ion-exchanged montmorillonite, pillared layered clays) are very active and, in general, selective in transforming primary, secondary, and tertiary aliphatic alcohols to 1-alkenes [39-43]. Al -exchanged montmorillonite, however, induces ether formation from primary alcohols and 2-propanol [41]. Substituted 1-phenyl-1-ethanols yield the corresponding styrene derivatives at high temperature (653-673 K) [44]. 

Other papers of interest in this section report transamination of camphor-3-carbothioamides with secondary cyclic amines, reaction of camphorquinone with dimethyl /S-ketoglutarate, the use of fenchone (212 X=0) in alkene formation from Grignard reagents, bromination of 2-e/itfo-6-endo-dibromobornane to yield 2,3,6-endo-tribromoborn-2-ene, and camphor-enol trimethylsilyl ether formation by quenching the reaction mixture of butyl-lithium and camphor tosyl-hydrazone with trimethylsilyl chloride. ... 

The direction of elimination of the /1-hydrogen to give either enol ethers or allylic ethers from alkenes can be controlled by using DMSO as a solvent. Formation of the allylic ether 47 was utilized in the synthesis of the tetronomycin precursor 47 from 46 [47], The oxidation of optically active 3-alkene-l,2-diol 48 afforded the 2,5-dihydrofuran 50 with high ee. It should be noted that /1-OH in 49 is eliminated to... 

Surprising results have been encountered in the hydrogenolysis of enamines to alkenes in the course of their reduction with an 1 1 mixture of lithium aluminum hydride and aluminum chloride in ether.301 From 1-pyrrolidinocyclopentene, 83% of cyclopentene was thus obtained. Formation of a-pyrrolidinocyclopentylaluminum chloride on addition of monochloroaluminum hydride to the enamine must be postulated, followed by decomposition of the intermediate complex to the cyeloalkene. The single known instance of reduction of a free enamine is represented by the reaction with dichloroaluminum hydride.302 Addition of the reagent leads to a complex which, on decomposition with water, affords the saturated base (Scheme 12). 

Both (1) and (2) convert alcohols, even tertiary ones, into the corresponding silyl ethers in the presence of pyridine without formation of alkenes the reaction is more rapid than that with t-butyldimethylsilyl chloride. The ethers derived from 2 are unusually stable they are not cleaved by CsF in DMSO even at elevated temperatures. But they can be cleaved by BF3 etherate in CH2CI2 at 0° to give borate ethers, which can be hydrolyzed by NaHC03 at 0°. 

After PCDEs were detected in a fly ash from a municipal waste incinerator in Finland [36], the occurrence of PCDEs in combustion wastes has not been studied much. PCDEs could be formed during incomplete combustion by condensation from chlorophenols as has been indicated for PCDDs [54], but de novo synthesis is also possible [55]. The formation of chlorinated compounds is always possible during combustion in the presence of organic material and chloride. The formation of PCDEs de novo in combustion has been described in the literature review of Kurz s thesis [4]. Briefly, diphenyl can be formed from the phenoxy radical and benzene which in turn can be formed from alkene radicals. If the formed molecule does not already contain chlorine, chlorination of diphenyl ether can occur, e.g., in the presence of HCl. It has been suggested, however, that PCDEs, in contrast to PCDDs and PCDFs, are not formed to a great extent de novo on solid surfaces or in the gas phase in thermal processes during metal reclamation processes [56]. When PCDEs were analyzed in emission samples of a metal reclamation plant in Finland, all PCDEs were below 4 ng nr3. 

Phenols are used as the nucleophile in the asymmetric aUylation of 7r-aUylpalladium complexes. Trost and Toste attained asymmetric phenyl ether formation in high enantiomeric excess (ee) using diphosphine ligand derived from chiral 1,2-cyclohexanediamine (equation 10). Dynamic kinetic resolution of the racemic secondary aUylic carbonate is conducted in the presence of tetrabutylammonium chloride, which increases the rate of ft—a—ft isomerization of the jr-allyl palladium intermediate (equation 11). Lautens and coworkers cleaved meio-oxabicyclic alkenes with phenol in the presence of a catalytic amount of a chiral ferrocenyldiphosphine and a rhodium complex (equation 12). ... 

Enol ester formation from crotonaldehyde gives the expected / -selectivity 66. Now the silyl enol ether is formed from this ester, also with the expected double bond geometry. The product 67 has three alkenes each is conjugated with at least one oxygen atom. 

With 1 as catalyst, alkene bonds which have oxidation potentials less than 1.6 V (vs standard calomel electrode) are considered potentially susceptible to this transformation. With the stronger oxidant 2, the scope of the reaction can be extended to include, for example, tetraalkyl-substituted double bonds, but obviously not disubstituted alkenes such as cyclohexene. On the other hand, electron-rich alkenes such as enol ethers and vinyl sulfides cannot be cyclo-propanated by this method. In order to suppress cyclodimer formation from the alkene and its radical cation, the diazo ester is sometimes applied in a four- to fivefold amount with respect to the alkene. 

With unsymmetrical alkenes, there are two regioisomeric meta adducts,1154 1160 1161 which are easily understood as the consequences of bond formation from the diradical intermediates 8.138 and 8.141, with the isolated radical centre forming a bond to either end of the allyl radical with little selectivity stemming from the presence of the substituent on the alkene. The low degree of selectivity is equally accommodated by a concerted reaction in which there is no intermediate. The main effect of having an electron-donating group, as in the reaction with ethyl vinyl ether 8.76, is that the ortho adduct 8.131 is the major product. The meta adducts 8.142-8.145 (R = OEt) are minor products (ortho.meta 65 35). With the rather less effective donor substituent, as in the reaction with vinyl acetate, the meta adducts 8.142-8.145 (R = OAc) are the major products (meta ortho 88 12). They show some selectivity in favour of the endo adducts (64 36 for R = OEt), and the major product 8.142... 

Recent data, published and unpublished, provide strong evidence that the common views on the reaction mechanism of the MTH reaction are not tenable. The data rather point to ethene and propene formation from an adsorbate hydrocarbon pool, probably of aromatic nature. There are strong indications that the catalytic cycle is based on arenes that are continually methylated by methanol/dimethyl ether, and dealkylations leading to ethene, propene and most likely also isobutene via molecular rearrangements. Penta- and hexamethylbenzene appear prone to undergo this reaction. However, there is also clear evidence that higher alkenes, if present in substantial amount, may take part in the classical homologation system. 

Carbon-Oxygen Bond Formation. CAN is an efficient reagent for the conversion of epoxides into /3-nitrato alcohols. 1,2-cA-Diols can be prepared from alkenes by reaction with CAN/I2 followed by hydrolysis with KOH. Of particular interest is the high-yield synthesis of various a-hydroxy ketones and a-amino ketones from oxiranes and aziridines, respectively. The reactions are operated under mild conditions with the use of NBS and a catalytic amount of CAN as the reagents (eq 25). In another case, N-(silylmethyl)amides can be converted to A-(methoxymethyl)amides by CAN in methanol (eq 26). This chemistry has found application in the removal of electroauxiliaries from peptide substrates. Other CAN-mediated C-0 bondforming reactions include the oxidative rearrangement of aryl cyclobutanes and oxetanes, the conversion of allylic and tertiary benzylic alcohols into their corresponding ethers, and the alkoxylation of cephem sulfoxides at the position a to the ester moiety. 

Arylthallium bis(trifluoroacetate)s are converted by successive treatment with KF and BF3 into aryl fluorides.Thallium(iii) nitrate (TTN) readily oxidizes dialkyl sulphides and selenides to the corresponding sulphoxides or selenoxides, and 2-(alkylthio)-l-arylethanones (37) into compounds (38) in methanolic solution.In a modification of the TTN oxidative conversion of aryl alkyl ketones into arylacetic acids, enol ethers derived from the ketones are used instead of the ketones themselves. This reduces the formation of side products. Cyclic aralkyl ketones (39) may be ring-expanded and alkylated to give compounds (40) via treatment of their Wittig-derived alkenes with TTN/ an extrapolation of the basic reaction discovered previously. 

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