Cyclization of 2-(3-butenyl)bromobenzene via the aryllithium derivative (original) (raw)
Related papers
The unexpected effects of added ligands on the addition of phenyllithium to E-cinnamaldehyde in THF
Arkivoc, 2006
The effect of donor ligands, usually expected to enhance the reactivity of organolithiums, was studied on the addition of PhLi to E-cinnamaldehyde in THF, under conditions that lead the reaction toward the production of 1,3-diphenylpropanone. It was observed that in the presence of TMEDA and HMPT, the rate of that reaction becomes slower than in the absence of ligands; the effect of HMPA was even more spectacular, at concentration [HMPA]: [PhLi] ≥ 4 the reaction becomes almost completely inhibited. These results show the complexity of solvation effects on the reactions of organolithiums and how substrate-reagent-ligand-solvent interactions are usually specific for the system under study.
A dramatic solvent effect on the stability and kinetics of intramolecular cyclization is described for the aryllithium species generated from 2-bromo-4,5-dimethoxy-(2-bromoethyl)benzene. The aryllithium generated by the halogen-metal exchange reaction with n-butyllithium, is stable for > 1h when generated at -95 to -100 oC in diethyl ether/hexane and can be trapped with electrophiles. However, when the reaction is conducted in a THF/hexane mixture, the intermediate undergoes instantaneous intramolecular cyclization to afford 4,5-dimethoxybenzocyclobutene. By comparison, the corresponding 1-lithio-2-(2-bromoethyl)-benzene intermediate is stable for >1h in either THF/hexane or diethyl ether/hexane at -95 to -100 oC. These results indicate that substituent effects as well as the nature of aggregation of these intermediates play key roles in determining the reaction pathway of functionalized aryllithium intermediates when quenched with electrophiles.
Tetrahedron, 1992
Key Wordr~ sequential radical reactions; 3 +2 cycloadditions; S-phenylthio-3-pentenyl radicals, thiohydmxamic esters of 6-phenylthio4hexenoic acids. Abstmct: Sequential radical a&iition/5-exo-cyclization&elimination reactions, accomplished by therm&y or photolyticalty induced decompositions of 0-acyl derivatives of N-hydroxypyridine-2-thione or other thiohydroxamic esters of 6-phenylthio-4-herenoic acids II in the presence of an excess of radicophilic ole~ns, afforded the 2vinylcyclopentanc den'vatives 13 in 5090% yields, while decompositions of thiohydroxamic esters or 6-phenylthio-4-hexynoic acids 24, under the same experimental conditions and in the presence of electron deficient oleflts, affordedthecorre.vponding2-vinylidenecyclopentane (2-o-alleniccyclopentane)derivatiws25 @I-72%). However, when &compositions of thiohydroxamic esters 39 were carried out in boiling toluene solution without rodicophilic olefins. 3-e-co-cyclization took place and the corresponding 2-vinylcyclopropane der&tives 40 were obtained in 43-60% yields. Tandem sequence of radical addition/cyclization reaction represents a simple and very useful methodology for annulation of polysubstituted cyclopentane rings. te3 Starting from two appropriate unsaturated synthons 1 and 2, by this sequence of reactions, 3 + 2 cycloaddition takes place involving two carbon-carbon bonds formations. 134*5 In addition to the tandem sequences4*6-'6. higher sequential radical transformations were Scheme 1. systematically investigated by designing the appropriate substrates, selection of reaction conditions and reagents, and following sequences such as additionlcyclizationladdition, 1*2 addition/cyclization/atom transfer17 and fragmentation/addition/cyclization'8 were successfully applied in the synthesis of complex polycyclic compounds. t6 In all of these sequential radical reactions several radical intermediates were involved in the propagation step of these radical chain reactions. The reactivities of the intermediary radicals involved in the key sequence, e.g. addition/cyclization, have to be in accordance with the reactivity of the corresponding unsaturated bonds,"
Tetrahedron, 2002
radical chain reactions of a variety of acyclic and cyclic a-azido ketones with tributyltin hydride have been investigated. The derived N-(tributylstannyl)aminyl radicals normally undergo H-abstraction reaction yielding corresponding amines, and thence symmetrical pyrazines by subsequent self-condensation, in competition with 1,2-H-migration from the a-carbon to nitrogen leading to a-imino ketone decomposition products with loss of the chain-carrying tributyltin radical. The noteworthy occurrence of a quite uncommon radical 1,2hydrogen-atom shift is considered to be largely due to consequent formation of a highly stable, captodative carbon-centred radical. In contrast with our previous N-stannylaminyl radicals produced from a-azido-b-keto esters, the present aminyl congeners give poor amounts (or even none) of nitrogen-inserted amides/lactams, which are envisaged to arise from intramolecular three-membered cyclisation onto the ketone moiety followed by b-scission of the resultant alkoxyl radical. It is inferred that adequate stabilisation of the eventual ring-opened carbon radical be a major factor for the successful outcome of the regiospeci®c nitrogen insertion process. Evidence is also presented that chemoselective attack of tris(trimethylsilyl)silyl radical to the ketone oxygen of an a-azido ketone gives rise to deazidation as a likely consequence of b-elimination of azidyl radical by the ensuing a-silyloxyalkyl radical. X-Ray crystal structure analyses of the bromo ketone 5a, the azido ketone 5b, the caprolactam 22, and the pyrazine 26 have been performed.
The reaction of nitrosodicyclohexylamine with organolithiums
Journal of Physical Organic Chemistry, 2008
The effect of donor ligands, usually expected to enhance the reactivity of organolithiums, was studied on the addition of PhLi to E-cinnamaldehyde in THF, under conditions that lead the reaction toward the production of 1,3-diphenylpropanone. It was observed that in the presence of TMEDA and HMPT, the rate of that reaction becomes slower than in the absence of ligands; the effect of HMPA was even more spectacular, at concentration [HMPA]: [PhLi] ≥ 4 the reaction becomes almost completely inhibited. These results show the complexity of solvation effects on the reactions of organolithiums and how substrate-reagent-ligand-solvent interactions are usually specific for the system under study.