Experimental and theoretical study of substituent effects on3J(13C1-1H) coupling constants in 1-X-bicyclo[1.1.1]pentanes
摘要:
A series of 23 bridgehead-substituted bicyclo[1,1,1]pentanes were synthesized and the (3)J(C1-H) coupling constants determined from their proton-coupled C-13 NMR spectra. It was found that the values of the couplings are strongly dependent upon the type of substituent present, with powerful effects exerted by the halogens in particular. The IPPP-CLOPPA-INDO theoretical approach, which was employed to provide a measure of the extent of through-bond versus through-space transmission of coupling information, was found to give (3)J(C1-H) values in good agreement with experimental data. Empirical substituent parameter regressions were performed and found to be consistent with the CLOPPA description of the increase in both the through-bond and through-space contributions to the coupling. The substituent parameter regressional analyses also demonstrated that electronegativity effects play a predominant role in determining the magnitude of the couplings, particularly in those substrates in which the substituent is attached to the ring system by a second-row element.
Formation and Reactions of Bicyclo[1.1.1]pentyl-1 Cations
摘要:
The ionization of l-bicyclo[1.1.1]pentyl halides was shown to initially form the 1,3-bridged bicycle[1.1.1]pentyl-l cation. It appears to be a transition state that leads to the bicyclo[1.1.0]butyl-1-carbinyl cation which can be trapped with azide ion and can be directly observed by NMR in SO2CIF. Although the major products of solvolysis of the halides are 3-methylenecyclobutyl derivatives, the corresponding cation was calculated to have a significantly higher energy than the bicyclobutylcarbinyl ion. Therefore, the products are probably formed by an attack of the nucleophile on the latter ion, accompanied by bond migration. The bridgehead iodide reacts under solvolytic conditions with azide ion to form bicyclo[1.1.0]butyl-l azide as a product. It also reacts with potassium hydroxide to give [1.1.1]propellane, and the same reaction occurs on dissolving in acetonitrile or pyridine. The reaction of 1,3-diiodobicyclo[1.1.1]pentane with ethoxide ion also was found to give [1.1.1]propellane via a nucleophilic attack on one of the iodines. The propellane reacts with methyl hypoiodite to give 3-iodobicyclo[1.1.1]pentyl-l cation, which can react with methanol to give 3-methoxybicyclo[1.1.1]pentyl-l iodide and with azide ion to give 3-iodobicyclo[1.1.1]pentyl-1 azide. These data provide evidence for a discrete 3-iodobicyclo[1.1.1]pentyl-l cation intermediate. The effect of substituents on the rate of solvolysis of bicyclo[1.1.1]pentyl-l iodide was studied. With 3-aryl substituents, a value of rho = -1.7 was found, which is similar to that observed in the solvolysis of 3-arylcyclobutyl tosylates (rho = -1.6). The 3-substituted bicyclopentyl halides usually form the corresponding 3-methylenecyclobutyl cations rather than bicyclo[1.1.0]butyl-1-carbinyl ions, because most substituents will help stabilize the former type of ion.
Photoinduced Copper‐Catalyzed Coupling of Terminal Alkynes and Alkyl Iodides
作者:Avijit Hazra、Mitchell T. Lee、Justin F. Chiu、Gojko Lalic
DOI:10.1002/anie.201801085
日期:2018.5.4
We have developed a photoinduced copper‐catalyzed alkylation of terminal alkynes with primary, secondary, or tertiary alkyl iodides as electrophiles. The reaction has a broad substrate scope and can be successfully performed in the presence of ester, nitrile, aryl halide, ketone, sulfonamide, epoxide, alcohol, and amide functional groups. The alkylation is promoted by blue light (λ≈450 nm) and proceeds
Nucleophilic substitution in 1-substituted 3-iodobicyclo[1.1.1]pentanes. A new synthetic route to functionalized bicyclo[1.1.1]pentane derivatives
作者:James L. Adcock、Andrei A. Gakh
DOI:10.1021/jo00049a030
日期:1992.11
Nucleophilic substitution of the iodine in 1-substituted 3-iodobicyclo[1.1.1]pentanes [R = I (1), CF3 (2)] was investigated. The results of the reaction are strongly dependent on the nature of the nucleophile and the substituent. Whereas the trifluoromethyl derivative 2 is found to be inert in the reactions and gave substitution products only with organolithium reagents, the 1,3-diiodide 1 is much more reactive and affords normal substitution products with nitrogen bases and MeONa but gives [1.1.1]propellane with Grignard and organolithium reagents and with triaryl(alkyl)phosphines. Other synthesized 3-iodobicyclo[1.1.1]pentanes did not give substitution products. A general scheme for the transformations of 1 is also proposed.
Synthesis of Some Bridgehead-Bridgehead-Disubstituted Bicyclo[1.1.1]pentanes
作者:Ernest W. Della、Dennis K. Taylor
DOI:10.1021/jo00090a015
日期:1994.6
The synthesis of a wide variety of 1,3-disubstituted bicyclo[1.1.1]pentanes is described, with particular emphasis on the generation of a series of S-X-substituted bicyclo[1.1.1]pentyl bromides required for solvolytic studies. Functional group manipulation at the bridgehead was readily accomplished in the majority of cases by radical processes in some instances, transformations were effected via carbanionic-type intermediates.