Methanol olefin elimination

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

Pyrano[3,4-i]indol-3-one (329) enters the Diels-Alder reaetion with methoxy-butenone as an eleetron-rieh olefin [92JCS(P1)415]. After deearboxylation of the primary adduet330,2-aeetyl-3-methoxy-l, 9-dimethyl-2,3-dihydroearbazole (331) eliminates methanol to form 2-aeetyl-l,9-dimethylearbazole (332) [92JCS (Pl)415]. 

Pyrolysis of bis(trimethylsilyl)phenyl methanol 1668 at 500 °C leads, via elimination of trimethylsilanol 4, to the carbene intermediate 1669, which rearranges, via the carbene intermediate 1670, to give l,2-dimethyl-2,3-benzo-l-silacyclopent-2-ene 1671, in 25% yield, or rearranges via olefin 1672 and adds 4 to give the siloxane 1673 in 29% yield and smaller amounts of benzyltrimethylsilane 83 and styrene [43, 44]. Pyrolysis of l,l-bis(trimethylsilyl) cyclohexylalcohol 1674 furnishes, via the carbene intermediate 1675, 90% of olefin 1676 [43, 44] (Scheme 10.20). 

Historically, the rhodium catalyzed carbonylation of methanol to acetic acid required large quantities of methyl iodide co-catalyst (1) and the related hydrocarboxylation of olefins required the presence of an alkyl iodide or hydrogen iodide (2). Unfortunately, the alkyl halides pose several significant difficulties since they are highly toxic, lead to iodine contamination of the final product, are highly corrosive, and are expensive to purchase and handle. Attempts to eliminate alkyl halides or their precursors have proven futile to date (1). 

Table 11. Carbonyl olefination according Scheme 46, method A 54) (elimination of G-OH by excess of perchloric acid in methanol at 20°C)...

Another possible reason that ethylene glycol is not produced by this system could be that the hydroxymethyl complex of (51) and (52) may undergo preferential reductive elimination to methanol, (52), rather than CO insertion, (51). However, CO insertion appears to take place in the formation of methyl formate, (53), where a similar insertion-reductive elimination branch appears to be involved. Insertion of CO should be much more favorable for the hydroxymethyl complex than for the methoxy complex (67, 83). Further, ruthenium carbonyl complexes are known to hydro-formylate olefins under conditions similar to those used in these CO hydrogenation reactions (183, 184). Based on the studies of equilibrium (46) previously described, a mononuclear catalyst and ruthenium hydride alkyl intermediate analogous to the hydroxymethyl complex of (51) seem probable. In such reactions, hydroformylation is achieved by CO insertion, and olefin hydrogenation is the result of competitive reductive elimination. The results reported for these reactions show that olefin hydroformylation predominates over hydrogenation, indicating that the CO insertion process of (51) should be quite competitive with the reductive elimination reaction of (52). 

In the case of certain diolefins, the palladium-carbon sigma-bonded complexes can be isolated and the stereochemistry of the addition with a variety of nucleophiles is trans (4, 5, 6). The stereochemistry of the addition-elimination reactions in the case of the monoolefins, because of the instability of the intermediate sigma-bonded complex, is not clear. It has been argued (7, 8, 9) that the chelating diolefins are atypical, and the stereochemical results cannot be extended to monoolefins since approach of an external nucleophile from the cis side presents steric problems. The trans stereochemistry has also been attributed either to the inability of the chelating diolefins to rotate 90° from the position perpendicular to the square plane of the metal complex to a position which would favor cis addition by metal and a ligand attached to it (10), or to the fact that methanol (nucleophile) does not coordinate to the metal prior to addition (11). In the Wacker Process, the kinetics of oxidation of olefins suggest, but do not require, the cis hydroxypalladation of olefins (12,13,14). The acetoxypalladation of a simple monoolefin, cyclohexene, proceeds by trans addition (15, 16). 

Preliminary observations indicate that the resulting secondary alkyls isomerize cleanly to the corresponding n -alkyls in dichloromethane-methanol, suggesting that the hydride ligand in the presumed cationic hydrido-olefin intermediate must return to the olefin more rapidly than it undergoes reductive elimination with the cr-alkyl or o -phenyl... 

Carbonyl olefination.1 The reaction of 1 with benzaldehyde results in a 1 1 separable mixture of the threo- and eryfAro-adducts (2a and 2b, respectively). The adducts undergo stereospecific ypn-elimination when heated to give /i-phenyl-thiostyrene (3). The (E)-isomer (3a) is formed from 2a, and the (Z)-isomer (3b) is formed from 2b. On the other hand, anfr -elimination obtains on treatment of 2 with perchloric acid in methanol. This carbonyl olefination has one advantage over the Peterson reaction in that intermediate adducts can be isolated and converted as desired to an (E)- or a (Z)-olefin. 

Ethers. Fluoro ethers have been obtained either by replacement, such as the formation of CF3OCH3 from the trichloro derivative,98 or by the action of alcoholic potassium hydroxide, upon a polyhalide. Example are CHBrFCF2OCH3 from CHBrFCF2Br,M and CH2FCF2OCH3 from CH2FCF2Br and methanolic potassium hydroxide.94, It is to be noted that the use of alcohols with longer chains minimizes the importance of the ether formation and favors the elimination of one molecule of halogen acid, with consequent formation of an olefin. 

The reaction of propylene with "phenylpalladium acetate has yielded information on the preferred mode of elimination as well as addition 24>. The reaction products found in methanol solution at 30 °C consisted of a 66% yield of a mixture of olefins containing... 

Further information on the mechanisms of these addition reactions is found in a study of the reaction of "phenylpalladium acetate with trans- and cfs-propenylbenzene 24>. The trans-isomer reacted in nearly quantitative yield at 30 °C in methanol solution to produce trans-1,2-diphenyl-l-propene. About a half of a percent yield of l,2-diphenyl-2-propene was also found. Only a trace of the Markovnikov product 1,1-diphenyl-l-propene was seen (See Chart 1). The reaction of cfs-propenyl-benzene under the same conditions produced an 85% yield of olefins containing 65% of cis- 1,2-diphenyl- 1-propene, 22% trans-1,2-diphenyl-1 -propene, 10% 2,3-diphenyl-l-propene and about 3% of 1,1-diphenyl-1-propene. The major products in both reactions are the one expected from a cis-anti-Markovnikov addition of the phenylpalladium acetate followed by a cis-elimination of "hydrodopalladium acetate . There is practically no Markovnikov addition. 

When primary alkyl phenyl tellurium or secondary alkyl phenyl tellurium compounds in methanol were treated with an excess of 3-chloroperoxybenzoic acid at 20, the phenyltelluro group was eliminated and replaced by a methoxy group. This reaction, which converts alkyl halides used in the synthesis of alkyl phenyl telluriums to alkyl methyl ethers, produced the ethers in yields as high as 90%3-4 Olefins are by-products in these reactions4 With ethanol as the solvent, ethyl ethers were formed. Other oxidizing agents (hydrogen peroxide, ozone, (ert.-butyl hydroperoxide, sodium periodate) did not produce alkyl methyl ethers. 

As indicated in Scheme VII/32, cyclononanone (VII/165) is transformed into hydroperoxide hemiacetal, VII/167, which is isolated as a mixture of stereoisomers. The addition of Fe(II)S04 to a solution of VII/167 in methanol saturated with Cu(OAc)2 gave ( )-recifeiolide (VII/171) in quantitative yield. No isomeric olefins were detected. In the first step of the proposed mechanism, an electron from Fe2+ is transferred to the peroxide to form the oxy radical VII/168. The central C,C-bond is weakened by antiperiplanar overlap with the lone pair on the ether oxygen. Cleavage of this bond leads to the secondary carbon radical VII/169, which yields, by an oxidative coupling with Cu(OAc)2, the alkyl copper intermediate VII/170. If we assume that the alkyl copper intermediate, VII/170, exists (a) as a (Z)-ester, stabilized by n (ether O) —> <7 (C=0) overlap (anomeric effect), and (b) is internally coordinated by the ester to form a pseudo-six-membered ring, then only one of the four -hydrogens is available for a syn-//-elimination. [111]. This reaction principle has been used in other macrolide syntheses, too [112] [113]. 

First, following the results of the 1,6-dioxa-spiro[2.5]octane rearrangement (5,19), continuous gas phase conditions were applied in a fixed bed reactor and secondly under liquid phase conditions in a slurry reactor. The catalytic experiments carried out showed that two main reactions took place rearrangement of 18 to the aldehyde 19 and a oxidative decarbonylation reaction to the olefine 1,3,3,4-tetramethyl-cyclohex-l-ene 20, which is assumed to be caused by a formaldehyde elimination reaction. Also observed was a deoxygenation reaction to the alkane 1,1,2,5-tetra-methylcyclohexane 21 (Eq. 15.2.7), explained by elimination of CO. There are several other side-products such as 2,2,3,6-tetramethylcyclohex-l-enyl-methanol, ringcontracting compounds and double bond isomers of dimethyl-isopropylene-cyclopentene. 

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