Meerwein s salt

Reaction of 2-ethoxycarbonyl-l-phenylpyrazolidine with Meerwein s salt (boron trifluoride etherate) yields the quaternary ammonium salt (426) which is not stable and undergoes ring opening to the hydrazine (427) with sodium ethoxide (76JOC1244). 

Substituted gulonolactones failed to react with Meerwein s salt. ... 

Substituted azocine systems are much more stable than the parent compound, and 2-methoxy derivatives have been intensively examined. Starting from cyclohexa-1,4-diene (3), a [2 + 2] cycloaddition with chlorosulfonyl isocyanate, followed by removal of the chlorosulfonyl group, leads to the /3-lactam 4, which can be transformed by O-methylation with Meerwein s salt into the corresponding imidate. Monobromination with A-bromosuccinimide and subsequent treatment with base results in a methoxyazabicyclo[4.2.0]octatriene derivative, which spontaneously isomerizes to 2-methoxyazocine (5).13,14... 

With Meerwein s salt, the products of the syntheses described in Section 1.1.1.1.3. can be transformed into the corresponding imidates.27... 

Alkylation of the pyridine-like nitrogen in 1 with the Meerwein s salt allowed the preparation of a derivative 2 of this ring system suitable for the evaluation of intercalating properties (Scheme 1) <2000BML1767, 1996BML2831>. 

These salts belong to a widely used class of alkylating agents their traditional name is Meerwein s salts (Meerwein et al. 1937). However, they can be involved in reactions other than alkylation (Boettger et al. 1997). One of these reactions is the oxidation of aromatic donors (Rathore et al. 1998a, Rathore and Burns 2003) ... 

In 1976, the synthesis of oxaziridininm salt 66 was reported by Lusinchi and coworkers (Fig. 23) [128-130]. Salt 66 was obtained by either methylation of the corresponding oxaziridine with FSO Me or oxidation of the corresponding iminium salt with peracid. Subsequently, Hanquet and coworkers prepared oxaziridininm salt 67 by methylation of the corresponding oxaziridine with Meerwein s salt (MejO BF ") or oxidation of the A -methyl isoquinoUnium fluoroborate salt with peracid [131, 132],... 

In 1993, Bohe and coworkers synthesized enantiomerically pure oxaziridinium salt 71 by methylation with Meerwein s salt and oxidation with mCPBA from dihydr-oisoquinoline 68 (Scheme 13) [136,137], Alternatively, 71 could also be produced by switching the reaction order. Epoxidations were carried out with either... 

The alkylation of the 2(3/f)-oxazolones 289 with Meerwein s salt (Et30 BF4 ) occurs readily and in excellent yield, thus providing an efficient route to the 2-ethoxyoxazoles 290. Although the yield of 290 (R = Me) is low, the process can be carried out on large scale starting from commercially inexpensive acetoin (Fig. 5.69). ... 

Thionolactones.1 Lactones can be converted into thionolactones by O-alkylation with Meerwein s salt followed by reaction with sodium hydrosulfide in acetonitrile. Hydroxy thionoesters are usually formed as by-products. 

An enantioselective synthesis of CR)-amino acids has been developed which utilizes L-valine as the chiral auxiliary (81AG(E)798). The diketopiperazine cycZo-(L-Val-Gly) (780) was converted to its bis-lactim ether (781) by methylation with Meerwein s salt, and the ether metallated in the glycine portion by n-butyllithium. Alkylation of the delocalized... 

The bc portion (267) was synthesized (Scheme 19) by treatment of the ethyl ester of i3, 3-dimethyllevulinic acid with hot ethanolic ammonia, followed by pyrolysis to give (275). Meanwhile, treatment of /8, 8-dimethyllevulinic acid with thionyl chloride gave the butyrolac-tone (276), and the sodium salt of this was treated with (275) to give (277). Photochemically induced acyl migration gave (278), which was treated with methanolic ammonia subsequent dehydration afforded (279), which was then activated by O- ethylation with Meerwein s salt to give (267). 

The cyanobromide (371) was condensed with the bc portion (347) to give the thioether (372) sulfide contraction to give (373) was accomplished using tris(/3-cyanoethyl) phosphine, and with phosphorus pentasulfide the thiolactam-thiolactone (374) was produced. After treatment with Meerwein s salt, reaction with dimethylamine opened the lactone with concomitant formation of an exocyclic methylene group, and subsequent treatment with cobalt chloride or iodide gave the chelate (375) which was reacted with diazabicyclononane to give bisnorcobyrinic add [Pg.435]

Dinitriles 97 on treatment with bases gave iminopyrrolizines 98a or aminopyrrolizines 98b.67,68 Imine 98a (R = piperidyl) formed a salt (99) with methyl iodide or with Meerwein s salt. Substitution of the dimethylamino group to give derivatives 100 is easily achieved67 (see Section III). 

Alkylation of 5-alkyl or 5-(arylsulfanyl)-l,2,3,4-thiatriazoles 9 (R = Alk, ArS) with Meerwein s salt produces 3,5-disubstituted thiatriazolium salts 31, although the 5-amino derivatives 9 (R1 =NHR2) are exclusively alkylated by... 

An enamine is ideal for the conjugate addition. We could have used diazomethane for the ring expansion but a better idea is to make it intramolecular by using a diazoketone 28 easily made from the free acid 27 with diazomethane. This time the rearrangement was initiated with Meerwein s salt and only the more substituted carbon atom migrates.4... 

Beside redox reactions, the S-l atom of penams can also be alkylated or chlorinated. On the one hand, by using Meerwein s salt or methyl fluorosulfonate, a series of methyl penicillanates have thus been S-methylated and their corresponding sulfonium salts 7 isolated and characterized (Figure 2) <1977TL71>. On the other hand, the use of sulfuryl chloride in carbon tetrachloride on the 6-unsubstituted methyl penicillanate led to the chlorosulfonium... 

Mixed bis-lactim ethers of type (20) are best prepared by the following route, outlined for the bis-lactimether (20a) of Cyclo(L-Val-Ala). L-Val, the chiral auxiliary, is converted with phosgene into its N-carboxyanhydride (L-Val-NCA, Leuchs anhydride) (17)l5). This gives with D,L-Ala-OCH3 the dipeptide (18) which on heating in toluene cyclizes to the diketopiperazine (19). This is converted into the bis-lactim ether (20a) [(3RS, 6S)-2,5-dimethoxy-6-isopropyl-3-methyl-3,6-dihydropyra-zine] with methyl Meerwein s salt. 

The nearly planar structure of Pd(II) complex 123 enabled a twofold connection of the bicyclic units in imino ether condensations brought about by Meerwein s salt and diisopropylethylamine in methylene chloride. Protonation of 124 (Scheme 14) generates a Pd(II) complex (125) of an octahy-droporphyrin, with complete saturation of the peripheral double bonds containing the 7t-system of l,5,9,13-tetraaza[16]annulene (68AG622). 

This reaction is an equilibrium and it may be necessary in making sulfonium salts from less reactive sulfides (sterically hindered ones for example) to use more powerful alkylating agents with non-nucleophilic counterions, for example, Me30+ BF4, trimethyloxonium fluoroborate (also known as Meerwein s salt). The sulfur atom captures a methyl group from 0+, but the reverse does not happen and the BF4 anion is not a nucleophile. 

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