John J. Eisch

Proposed radical pathway for the additon of allyl grignard reagents to conjugated anils

The products from the individual reactions of allylmagnesium bromide with 2-styrylpyridine, with 4-styrylpyridine and with α-allylbenzhydrylaniline,rrespectively, were examined, in order to test the possible role of electron-transfer processes both in the addition and elimination steps of Grignard reagent-anil interactions. In contrast with the smooth 11 adduct of the Grignard reagent with the exocyclic double bond of 2-styrylpyridine, the corresponding reaction with 4-styrylpyridine led principally to oligomeric and/or polymeric adducts. Moreover, heating α-allylbenzhydrylaniline in benzene with an excess of the Grignard reagent led to benzhydrylaniline,ssuggestive of C-C bond homolysis. The results, taken together with other information on Grignard reagent-anil interactions, are consistent with a radical mechanism, possibly initiated by electron transfer.

Bora-aromatic systems I. Competition between haloboration and phenylboration in the attempted synthesis of triphenylboracyclopropene☆☆☆

A possible tactical approach to the synthesis of triphenylboracyclopropene (triphenylborirene) is described as involving: (a) the addition of phenylboron dibromide to the triple bond of diphenylacetylene; and (b) the interaction of the resulting (cis-2-bromo-1,2-diphenylvinyl)phenylboron bromide with lithium metal in tetrahydrofuran at −77°. Factors determining the competition between BBr bond addition in step “a” and the slower BC6H5 bond addition to the triple bond are analyzed. By treatment of aliquots of the reaction product of steps “a” and “b” with alkyl halides, with carbon dioxide and with O-deuterioacetic acid, it is concluded that a stilbene derivative with vicinal cis-carbon-boron bonds has been formed. The nature of the organoborane precursor of cis-stilbene is discussed in terms of structural alternatives, such as triphenylborirene, hexaphenyl-1,4-diboracyclohexadiene or a polymer.

The question of allylic rearrangement in the reactions of tribenzylaluminum

Abstract In order to evaluate the structural factors leading either to normal or to allylic reactions with allylic carbon—aluminum bonds, the behavior of pure samples of tribenzylaluminum and of tribenzylaluminum diethyl etherate has been examined. Analysis of their NMR spectra as a function of temperature between +25° and −90° was consistent with the presence of monomeric, non-fluxional species. Their cleavage reactions under agency of deuterium oxide, diphenylacetylene, or ultraviolet radiation proceeded normally, while that with carbon dioxide occurred only with allylic rearrangement. The case of benzophenone anil was one where principally normal cleavage, succeeded by an elimination reaction, was observed.

Reinvestigation of apparent 1,4-addition and rearrangement in the reactions of quinolines with organolithium compounds

Abstract The recent claim of Otsuji, Yutani and Imoto7 that both n-butyllithium and phenyllithium gave isolable 1,4-adducts with lepidine (4-methylquinoline) has been reinvestigated. Such adducts were reportedly captured in the form of their N-ethoxycarbonyl derivatives. In the present study these same N-ethoxycarbonyl derivatives have been prepared and examined by NMR and IR spectroscopy. Moreover, the corresponding N-(ethoxycarbonyl)-n-butyldihydro and N-(ethoxycarbonyl)phenyldihydro derivatives have now been prepared from 2-deuteriolepidine. An analysis of the spectroscopic data leads to the clear conclusion that all such derivatives are really 2-substituted-1,2-dihydrolepidines. Consequently, all the discussion published in ref. 7, concerning a 1,4-addition of organolithium reagents to the quinoline nucleus and the subsequent rearrangement to the 1,2-adduct, becomes unfounded.

Halogenation of Heterocyclic Compounds

Publisher Summary The chapter focuses on the newer findings in the synthetic and mechanistic aspects of heterocyclic halogenation. Precise mechanistic descriptions of heterocyclic halogenation are not possible with the existing experimental information. Still it appears desirable to consider what mechanistic models may be involved in such substitution processes, in an attempt both to correlate what is known and to sharpen the focus of future research. In assessing the applicability of the foregoing model to a given heterocyclic halogenation, approaches such as the detection and isolation of intermediates, the kinetic behavior of these stable intermediates, possible kinetic isotope effects for deuterated heterocycles, and the kinetic response of halogenation to general base catalysis will prove especially valuable. The existing evidence on the mechanism of substitution is treated with reference to this model. The chapter discusses the nature of the reacting species in the reaction medium. Appreciable recent effort has been devoted to developing highly selective methods for halogenating heterocycles. As with most fields of chemical research, the synthetic aspects of heterocyclic halogenation have been mastered far better than have the underlying reaction mechanisms.

Selective phenylation of olefins with triphenylaluminum

Abstract The arylation of selected olefinic types of aluminum aryls was surveyed, as to feasibility and stereoselectivity, by an examination of the behavior of triphenyl-aluminum toward 1,1-diphenylethylene, 1-octene, exo -5-phenylbicyclo[2.2.1] hept-2-ene, bicyclo[2.2.1]hepta-2,5-diene and indene, respectively, The first four substrates underwent phenyl  bond addition with a reactivity increasing in the order given; but indene suffered only metallation. The variation in olefin reactivity, the stereo- and regio-specificity, and the metallation of indene and cis -stilbene seem to best explained by means of electrphilic attack by aluminum on carbon, proceeding through a π or σ-complex.