Alkyl elimination

It has been tentatively suggested that one mechanism underlies the Willgerodt reaction and the Kindler modification of it. A labile intermediate is first formed which has a carbon—carbon bond in the side chain. The scheme is indicated below it postulates a series of steps involving the addition of ammonia or amine (R = H or alkyl), elimination of water, re addition and eUmination of ammonia or amine until the unsaturation appears at the end of the chain then an irreversible oxidation between sulphur and the nitrogen compound may occur to produce a thioamide. 

The desulfiirisation of sultones results in the formation of an exocyclic alkene and can be achieved by an alkylation - elimination procedure <96TL 1841>. 

An unusual one-pot intramolecular sulfoxide alkylation-elimination reaction was found by Gibson et al. <2001SL712>. These authors found that treatment of 459 with potassium bis-trimethylsilylamide resulted in a ring closure to 460 in acceptable yield. Furthermore, Batori and Messmer found an effective method for preparation of [l,2,3]triazolo[l,5- ]pyrimidinium salts <1994JHC1041> oxidative cyclization of hydrazones 461 by 2,4,4,6-tetrabromo-2,5-cyclohexadienone gave rise to the quaternary salts 462. Under certain reaction conditions, the formation of 6-bromo-salts 462 (R6 = Br) was also experienced. As neither the starting compound nor the quaternary triazolopyridinium salt underwent bromination in this position, the authors assumed that this bromination process occurred on one of the intermediates in the course of the above-mentioned cyclization reaction. 

Although the amount of cracking was generally low, some comments can be asserted about the reactions taking place. The detection of diphenyl may indicate some cracking of H2P initially to form ethyldiphenyl or dimethyldiptenyl followed by alkyl elimination reactions. 

The stability of dialkylimidazolium cation-containing ionic liquids can be a problem even at moderate temperatures in the presence of some reagents or catalysts. For example, when CsF and KF were used in the ionic liquid [BMIM]PFg to perform a halogen exchange reaction in an attempt to replace Br from bromo-carbons with F , it was found that alkyl elimination from the [BMIM] cation took place, forming methyl imidazole, 1-butene, 1-fluorobutane, and other unidentified products at 150°C overnight 69). The fluoride ion acted as a base that promotes elimination or substitution processes. 

The goal of this investigation was to obtain enantiomerically pure oxovinylphosphoranes by an overall alkylation/ elimination sequence. Therefore, the diastereoselectivity of the alkylation with other alkyl halides was not evaluated. 

Catalytic hydrogenolysis of light alkanes (propane, butanes, pentanes) with the exception of ethane has been accomplished under very mild conditions over silica-supported hydride complexes.502 The hydrogenolysis proceeds over (=SiO)3 ZrH,503 (=SiO)3HfH,504 and (=SiO)3TiH505 by stepwise cleavage of carbon-carbon bonds by P-alkyl elimination from surface metal-alkyl intermediates. 

The reaction of trimethyl phosphate, (MeO)3PO, with NiBr2 results in the neutral bis-dimethoxyphosphato complex by elimination of one methyl group from the neutral phosphoric esters (equation 185).1708 But when nickel halides are reacted at higher temperatures with the neutral diisopropylmethylphosphonate, an alkyl elimination and a phosphato condensation occur (equation 186).1709... 

Watson et al.124-1261 studied the polymerization of ethylene and propylene with Lu(n5-C5Me5)2(CH3) ether in toluene or cyclohexane at 30-80 °C. The Lu complex produced polymers of Mn = 10M04 for ethylene, and oligomers for propylene. In the oligomerization of propylene an unusual chain transfer reaction due to 0-alkyl elimination was found together with P-hydrogen elimination from Lu-alkyls as chain-terminating processes 125). 

Still other epoxide cleavage processes can be nucleophile induced, but without direct attack at a heterocyclic carbon. A good illustration of this phenomenon is seen in the alkylative elimination of epoxy tosylhydrazones (62). Optically pure allyl alcohols have been prepared... 

Solid-liquid solvent-free phase transfer catalysis (PTC) is specific for anionic reactions including numerous alkylations, eliminations and anionic additions. The coupling of PTC conditions and microwave irradiation was applied to numerous alkylations, eliminations, anionic condensations, and... 

In the course of these studies key features such as olefin coordination [19,20], olefin insertion (propagation) [16,21,22], /(-hydrogen elimination [16,21,22], and /3-alkyl elimination [23] could be spectroscopically and structurally proven. In particular, yttrium aluminates have been proposed to model isoelectronic cationic homo- and heterobridged Zr/Al heterobimetallic complexes as dormant species and potential polymer chain transfer candidates [24]. Such zirconium aluminate complexes seem to be elusive [25], while the first structurally characterized titanium alumi-... 

Scheme 6.4 Generation of a palladium bis-imidazole complex via alkyl elimination...

The products can be converted into /,3-enyncs by sulfoxide elimination (equation I) or by alkylation-elimination (equation II 7, 149- i50). 

Oxidation of [Mo(NRAr)3] with pyridine N-oxide afforded the paramagnetic tetrahedral oxomolybdenum(V) compound [MoO(NRAr)3]. Alkyl elimination from this afforded [MoO(NAr)(NRAr)2] while oxidation gave [MoO(NRAr)3]+. 

Further studies 103) of this system showed that the latter reaction was reversible, i.e., /3-alkyl elimination was occurring [Eqs. (42) and (43)]. 

Except for a 1960 report on one alkylaluminum system 104), no /3-alkyl elimination reactions of this type had ever been observed. Thus, this reaction provided another example in which lanthanide systems demonstrated special organometallic chemistry. 

The synthesis of a number of phosphonate derivatives of methylenecyclo-propane nucleoside analogues (86a-l) has been reported by Zemlicka. Most were obtained by an alkylation-elimination approach. Starting from a meth-anesulfonate, methylenecyclopropane phosphonates were obtained by Michaelis-Becker reaction with alkyl phosphites and converted to vicinal dibromides, subsequently used for alkylation-elimination of nucleic acid type bases. All compounds were evaluated against herpes viruses, hepatitis B and HIV and were found to be inactive except for (86b), which was found to inhibit VZV proliferation. 

C5Mes)2Lu(R) complexes undergo all of the key reactions involved in olefin polymerization including olefin insertion (chain propagation), )7-H and ) -alkyl elimination, and Lu—R bond hydrogenolysis (chain transfer/ termination) (23). 

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