Nucleophilic attack of methoxide

The step common to both of these reactions is electrophilic attack of a hypervalent iodine species at the a-carbon of the carbonyl compounds to yield an intermediate 3. Nucleophilic attack of methoxide ion or tosy-loxy ion with the concomitant loss of iodobenzene results in a-functionalized carbonyl compounds (Scheme 2). 

Cacciapaglia, R., Lucente, S., Mandolini, L., van Doom, A.R., Reinhoudt, D.N. and Verboom, W. (1989) Catalysis by alkali and alkline-earth metal ions in nucleophilic attack of methoxide ion on crown ethers bearing an intra-annular acetoxy group. Tetrahedron, 45, 5293. 

Although some ylid formation undoubtedly occurs in these decompositions, it is not known whether the ether is formed by a carbenoid insertion into the 0—H bond of the alcohol 14 82> or by reprotonation of the ylid followed by nucleophilic attack of methoxide. Although other ylid decomposition products were sought, no evidence for their existence was observed 109). Several other reactions between alkoxides and the tetramethylammonium ion have been reported. The p-naphthoxide gives an 80% yield of the methylether on decomposition at 110 °C whereas the triphenylcarbinolate gives a 37% yield of the methylether and a 37% yield of the carbinol in boiling dioxane at 102 °C 162). 

Although the term methanol carbonylation is usually associated with acetic acid manufacture, an alternative carbonylation pathway involves base-catalyzed addition of CO to alkoxide ions to provide a simple route to formate esters (see also the section Direct Synthesis of Methanol from CO/H2). In the case of methanol as the alkanol, the reaction is carried out industrially on a large scale to produce formic acid. The reaction proceeds at ca 30 bar and 80°C using sodium or potassium methoxide as the catalyst and involves nucleophilic attack of methoxide on CO ... 

The cationic species [IrX2(CO)(PMe2Ph)3]+ (XVI, Q = CO) undergoes nucleophilic attack by methoxide forming the carboxylate complex (XXI). In the presence of very strong base, a cyclometallation of a methyl group occurs forming (XXIV) [165],... 

There is one report of competitive nucleophilic attack at the amide carbonyl in an Ai-acyloxy-A-aUtoxyamide. Shtamburg and coworkers have reported that MeONa reacted with Ai-acetoxy-A-ethoxybenzamide (159) in DME giving methyl and ethyl benzoate (160 and 161) (Scheme 26) . They attributed the formation of methyl benzoate to the direct attack of methoxide ion at the amide carbonyl rather than at nitrogen. The formation of 161 was attributed to a HERON reaction. Though not mentioned by the authors, it seems likely that under these aprotic conditions, 162 could also have been formed by methoxide attack at the acetate carbonyl leading to an anion-induced HERON reaction, by analogy with the reaction of Ai-acyloxy-Ai-alkoxyamides and aqueous hydroxide discussed above (Section IV.C.3.c)... 

The UV spectrum of 1-methylquinoxalium iodide in dilute aqueous alkali at pH 10.5 shows absorption maxima at 301 and 340 nm, and in methanolic sodium methoxide, maxima at 304 and 344 nm. The two maxima in aqueous alkali are attributed to the existence of an equilibrium mixture of the pseudobase 251 and the tetrahydroquin-oxaline 252. The pseudobase is the species that gives rise to the longer wavelength absorption maximum at 340 nm. It is formed by nucleophilic attack of hydroxide ion at C-2 in aqueous alkali, and the tetra-hydroquinoxaline is the result of covalent addition of water across the C3-N4 double bond of the pseudobase.251 A similar explanation is advanced for the two maxima observed in methanol with methoxide. 

Blout observed that the rate of polymerization of y-benzyl glutamic acid NCA was approximately 100-times faster when initiated with sodium methoxide rather than a primary or secondary amine.19,101 He proposed the active monomer mechanism of NCA polymerization previously formulated by Ballard and Bamford,1111 which involves the extraction of the proton from the NCA nitrogen to give anion 3, followed by nucleophilic attack of this anion on the amino acid carbonyl of a second NCA (Scheme 2). The active monomer mechanism was further studied and substantiated by Goodman.112-141... 

Intramolecular nucleophilic attack of the acidic methylene moiety at the dithiazole C-5 carbon atom of compounds 60 is carried out in the presence of sodium methoxide. After the ring opening and extrusion of one sulfur atom, products 61 are formed (Equation 7) <2005H(65)1295>. 

The 2-methyl-4/3,5/3-epoxy-3-ketone (244) reacts with methoxide ion to give the three products (245)—(247).208 A Favorskii-type rearrangement is clearly responsible for producing the A-nor-lactone (245), and is considered also to account for the other two products. The 2-methoxy-2-methyl-4-en-3-one (246), however, could possibly result from direct attack of methoxide ion on the A2-enol derivative of the epoxy-ketone (cine substitution), followed by elimination of a 5/3-hydroxy-group to give the a/3-unsaturated ketone. The occurrence of Favorskii rearrangement in the 2-methylated compound (244) contrasts with a simple nucleophilic opening of the unsubstituted 4/3,5/3-epoxy-3-ketone this is one of several recent examples in which an a-substituent favours Favorskii rather than alternative reactions.208... 

Of course, aziridines can also be synthesized by the ring-closing reactions of appropriately substituted amines. For example, halohydrins of type 142 are converted to iV-hydroxy-aziridines 144 by treatment with hydroxylamine derivatives, followed by base-catalyzed intramolecular Sn2 reaction of the intermediate p-haloaminoesters 143 under phase-transfer conditions <03TL3259>. A -Bromoethylimines 146, formed from the reaction of benzaldehyde derivatives (e.g., 145) and 2-bromo-2-methylpropylamine hydrobromide, undergo nucleophilic attack by methoxide, followed by intramolecular displacement of bromide to form A -(a-methoxybenzyl)aziridines 147 <03TL1137>. 

New C-0 bonds are formed in the CO/H2 synthesis when CO is converted to CO2 by the WGS reaction (3) and in the synthesis of esters. Only the latter will be discussed here. Primarily methyl esters are formed, and they are significant side products over the (Cs)/Cu/ZnO catalysts but not over the alkali/(Co)/M0S2 catalysts. The mechanism for methyl ester formation has been suggested (ref. 39) to occur via a coupling of a Cn aldehyde with a Ci aldehyde by the Cannizzaro reaction or by a nucleophilic attack of a Cn aldehyde by methoxide (Tischenko reaction). The exception is the formation of methyl formate that occurs via a nucleophilic attack of CO by adsorbed methoxide e... 

Triazine (1) is highly 7c-electron deficient and readily attacked by nucleophiles. The parent triazine (la) slowly decomposed in methanol at room temperature, which suggested that nucleophilic attack of methanol occurred in the solution. The NMR spectrum of (la) in CD3OD measured at — 50°C in the presence of a base indicated that attack of methoxide ion on the 4-position was succeeded by ring-opening accompanied by the elimination of nitrogen (Equation (14)) <92H(33)63l >. All attempts failed to oxidize the intermediate 1,4-dihydro adducts to form 4-substituted triazines. 

In order to craft the lactone ring, 38 was oxidized to 40 under Swem conditions in a prelude to intramolecular 1,4-addition of the hemiacetal anion [20] formed via nucleophilic attack by methoxide ion at the aldehyde site. With the availability of acetal 41, it became necessary to consider carefully whether to elaborate the epoxy lactone segment in advance of, or subsequent to, introduction of the a,p-unsaturated ester subunit. Since the latter option was considered more workable, 41 was transformed into the enol triflate and subjected to palladium(II) catalyzed methoxycarbonylation [21]. This methodology allowed for proper homologation of 42 to 43, and subsequent conversion to 44, in totally regiocontrolled fashion. 

All the polymers were reused after filtration to lest their possible recycling a permanent loss of base in polymers 39 and PTBD 4 was detected. This can be explained by a nucleophilic attack of the methoxide anion on the ben7> lic (Tl group of 44 that causes the leaching of the tetrameihylgiianidinc 46 and the subsequent production of the inactive polymer 45 (Scheme 11). 

The methoxycarbyne complex Tp W( = COMe)(CO)2 also reacts at the carbyne substituent with nucleophiles attacking the methoxide Me group, delivering Me and generating [Tp W(CO)3] via an Sn2 reaction.The reactivity of the methoxycarbyne complex Tp W( = COMe)(CO)2 thus differs considerably from that of the methylthiocarbyne complex Tp W( = CSMe)(CO)2, which reacts with phosphines at the carbyne carbon to undergo nucleophilic displacement of the methylthiolate substituent to produce phosphoniocarbyne complexes.The... 

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