Meerwein reagent

Treatment of the dithiete 175 with Meerwein reagent yielded the sulfo-nium salt 212 in high yield (99UP1). 

Yet another compound that exhibits antidepressant properties, that does not fit the classical mold, is a rather simple substituted ami dine. Reaction of amide with triethyloxoniurn fluoroborate (Meerwein reagent) affords the corresponding imino ether Exposure of this inter-... 

The groups of Trost and coworkers and Caserio and coworkers independently developed procedures for azasulfenylation. Caserio reported that when alkenes are treated with a sulfenamide such as MeSN-Me2 in the presence of the Meerwein reagent trimethyloxonium tetrafluoroborate, azasulfenylation of the alkene is observed, presumably via the thioammonium ion MeSNMe3+ (equation 4).20 Boron trifluoride etherate can also serve as a catalyst for addition of sulfenamides to alkenes. The adduct stereochemistry is strictly anti as established by treatment of the dihydropyran methanesulfenyl chloride adduct (see Scheme 2) with AgBF4 followed by trimethylamine. 

The unsaturated lactam ester 62 was also employed in a modified synthesis of ( )-lycorine (1) (109). In the event, O-ethylation of 62 with excess Meerwein reagent followed by reduction of the resulting imidate 77 with either sodium borohydride/stannic chloride dietherate (111) or sodium borohydride/stannous chloride gave an intermediate secondary amine, which cyclized on heating in methanol containing K2C03 to provide the lactam 78 (Scheme 5). When 78 was... 

The second total synthesis of cephalotaxine (157-159) was very different conceptually since it was a convergent synthesis involving the two intermediates 248 and 249. The azabicyclic intermediate (248) was prepared from pyrrolidone (250) (Scheme 52), which with the Meerwein reagent gave 251. The latter was treated with an excess of allyl Grignard reagent to yield 252. 

The next phase of the synthesis was installation of the dimethylamino-oxazoline ring system. This was constructed from the oxazolidinone precursor 19. Oxazolidinone formation occurred when 25 was reacted with thionyl chloride. The more nucleophilic carbonyl of 19 was then O-alkylated with the Meerwein reagent to give an iminium ion that readily participated in a nucleophilic addition/elimination reaction with dime-thylamine to give 26. The final step of the synthesis was O-deacetylation of 26 with sodium methoxide to provide (—)-allosamizoline hydrochloride in 98% yield after acidification. 

As early as 1974, Hanessian and Pemet [56] demonstrated the use of anion chemistry in the preparation of C-glycosides. As shown in Scheme 7.6, acetobromoglucose was treated with the anions of diethylmalonate and dibenzylmalonate, yielding two distinct C-glycosides. In the case of the dibenzyl analog, debenzylation, followed by treatment with the Meerwein reagent, gave a... 

Substituted thiolactams (65) are obtained from lactams (63) in SS-100% yield by alkylation with Meerwein reagent and subsequent thiolysis of the resulting imidium salt (64 equation 29). The ap-proach has been extended to other thiolactams and acyclic examples employing a cyanohydrin derivative (66 equation 30). Similarly, A, N-acetals of formyl cyanide, (R2N)2CHC N, yield thioformamides on treatment with HaS. ... 

Treatment of 4-acyl-1,2-dihydroisoquinolines, e.g., 125, with triethyl-oxonium tetrafluoroborate (Meerwein reagent) produced vinylogs of the ethoxyiminium cations in high yield, e.g., 126. Crystallization of 126 from methanol gave pure 127. In order to perform syntheses of 3-substituted ... 

The first compound having an ethyl side chain to be synthesized by this method was a compound in the pseudo -Aspidosperma series (204). The key compound in this sequence is the vinylogous amide 414, which was prepared from 2-hydroxytryptamine hydrochloride (406) and 3-oxobutanal ethylene ketal (407), followed by hydrolysis, cyclization with the Meerwein reagent, and acetylation (205). 

The most important aspect of this synthesis, though, is the extension to include jS-anilinoacrylate derivatives. Treatment of 542 with the Meerwein reagent gave the imino ether 545 in quantitative yield which, upon heating with sodium hydride in dimethyl sulfoxide at 115 for 2 hr, gave a 2 1 mixture of the 3-oxo derivatives 546 and 547, which were not separated at this point. 

If a reagent with an electrophilic C-atom is added instead of a proton to a a-diazo-)S-carbonyl compound a much more favorable equilibrium is obtained. Bott (1964, 1966) added the Meerwein reagent triethyloxonium hexachloroantimonate to ethyl diazoacetate (2.274) and to (4-nitrophenyl)-diazoacetic-acid piperide (2.276) and obtained the isolable alkenediazonium salts 2.275 and 2.277 (2-105 and 2-106). 

Complexes of type 10.61 can also be converted into isocyanide complexes (one X in 10.61 = C=N — C4H9) which, after reaction, first with A1(CH3)3 and second with trimethyloxonium salt (Meerwein reagent) and CO, yield, e.g., the alkyldi-azenidoaminocarbene complex 10.63 (Harada et al., 1994). 

In addition to the exchange reaction described previously, formamidines derived from secondary amines can be prepared by forming the N-formyl derivative, which is treated successively with boron trifluoride etherate and the appropriate primary amine (eq. 3, Table II). However, this method is not satisfactory if sensitive groups (e.g., Me3Si) are present on the amine since they are cleaved by the Meerwein reagent. 

Meerwein s salts, also known as the Meerwein reagent, refer to trimethyloxonium tetrafluoroborate (Me30 BF4 ) and triethyloxonium tetrafluoroborate (Et30 F4 ). Named after the inventor Flans Meerwein, these trialkyloxonium salts are powerful alkylating agents. 

Example 1, The Meerwein reagent is an excellent O-alkylating agent ... 

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