Trimethylamine deprotonation

The metallation of 3-methyl-4//-5,6-dihydro-l,2-oxazine has been shown to take place at the methyl group with hindered bases and at the methylene group with unhindered bases (81JA5916). Deprotonation of (753) with lithium dimethylamide at -65 °C followed by reaction with benzyl bromide gave (754) in 85% yield. This product was converted to enone (755) by reaction first with triethyloxonium tetrafluoroborate to produce an oxoiminium salt. The salt was stirred with trimethylamine and the resulting a,/3-unsaturated imine hydrolyzed with wet silica gel to the enone (Scheme 174). The lithiated derivative of (753) serves as a synthon for the unknown a-anion of methyl vinyl ketone. 

Deprotonation of t-amine oxides LDA (excess) converts trimethylamine oxide into a reactive ylide (a) that dimerizes to the dimethylpiperazine (2). If a is generated in the presence of an alkene, pyrrolidines (3) are formed via a 1,3-dipolar cycloaddition. The ylide reacts with cyclic alkenes to form bicyclic pyrrolidines in 40-90% yield.2... 

The rate constants for deprotonation of the trimethylamine radical cation by the parent amine and by hydroxyl radicals were estimated as 1 x 10 and 1 x 10 M s , respectively [84]. The rate constants for the different steps involved in the reaction of oxygen with a-aminoalkyl radical 31 (Scheme 7) were determined by pulse radiolysis with conductivity detection [85]. 

Substrate bond breakage by wild-type TMADH is too fast to be followed using the stopped-flow method in the regime where both His-172 and trimethylamine in the enzyme-substrate complex are deprotonated (that is pH 10). Consequently, our tunneling studies have focused on the compromised mutant enzymes H172Q and Y169F ( 10-fold and 40-fold reduction in the limiting rate constant for flavin reduction compared with wild-type enzyme, respectively). 

Yet another rather general approach towards highly substituted cyclopenta-dienones has been developed via /1-aminosubstituted a,/ -unsaturated chromi-umcarbene complexes such as 32. Their cycloaddition to alkynes proceeds without carbonyl insertion to yield 1,2,3-trisubstituted 5-dimethylamino-3-ethoxy-cyclopentadienes which are readily hydrolyzed to the correspondingly substituted cyclopentenones [26]. After quaternization with methyl iodide the ammonium salt 33 is obtained. Treatment of the latter with a base such as NaOMe or NaOH results in deprotonation and elimination of trimethylamine to yield a trisubstituted cyclopentadienone which immediately dimerizes by [2 + 2] cycloaddition probably via a 1,4-diradical intermediate like 35 to yield the bis(cyclo-pentenone)-annelated cyclobutane derivative 34 (Scheme 8) [27]. 

Amines deprotonate water to a small extent to form ammonium and hydroxide ions. Thus, amines are more strongly basic than alcohols but not nearly as basic as alkoxides. Protonation occurs at the site of the free electron pair as pictured in the electrostatic potential map of A,A-dimethylmethanamine (trimethylamine) in the margin. 

Stevens rearrangements proceed smoothly whenever a benzylic group is migrating. For example, ethereal phenyllithium readily deprotonates tetramethylammon-ium bromide to give the lithium bromide-complexed ylide. This species reacts with a variety of electrophiles such as benzophenone, methyl iodide, or molecular iodine. But when the suspension is shaken in a sealed tube for 90 h at ambient temperature, the ylide decomposes entirely to trimethylamine and polymethylene (up to 74%) irrespective of the solvent used (DEE, THE, glyme). The same kind of degradation occurs when phenyllithium is replaced by -butyllithium or phenylsodium. ... 

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