Sterically crowded bicyclo[1.1.0]butane radical cations

The variability of carbon-carbon single bonds by steric and electronic effects is probed by DFT calculations of sterically crowded bicyclo[1.1.0]butanes and their radical cations. The interplay of sterics and electronics on the gradual weakening and breaking of bonds was studied by investigating bridgehead substitution in 1,3-di-tert-butylbicyclo[1.1.0]butane and 2,2',4,4'-tetramethyl-1,3-di-tert-butylbicyclo[1.1.0]butane and geminal substitution in 2,2'-di-tert-butylbicyclo[1.1.0]butane and 2,2',4,4'-tetra-tert-butylbicyclo[1.1.0]butane. Bridgehead substitution leads to a lengthening of the central bond, whereas bisubstitution on the geminal carbon leads to a shortening of this bond due to a Thorpe-Ingold effect. Although the character of the central bond can be modulated by substitution and electron transfer over a range of 0.35 A, the state forbidden ring planarization does not occur. Sterically crowded bicyclo[1.1.0]butane radical cations are therefore promising candidates for the investigation of extremely long carbon-carbon single bonds.     

New synthesis of bicyclo[1.1.0]butane hydrocarbons

Conclusions A new general synthesis is proposed for bicyclo[1.1.0]butanes, by 1,3-cyclization of 1-bromo-chloromethylcyclopropanes, and a two-step synthesis of the latter from available allyl chlorides has been developed.Deceased.Translated from Izvestlya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2043–2047, September, 1985.     

Reaction of bicyclo [1.1.0] butane with mercury acetate

Russian Chemical Bulletin -     

A new method of synthesis of bicyclo[1.1.0]butane

Russian Chemical Bulletin -     

Additions of carbenes to 1,2,2-trimethylbicyclo[1.1.0]butane

Dicarbomethoxy- and dichlorocarbene add to 1,2,2-trimethylbicyclo[1.1.0]butane to give derivatives of 2,3,3-trimethylpenta-1,4-diene. These products are not predicted by the mechanism proposed earlier. A new mechanism is suggested.     

Unsubstituted bicyclo[1.1.0]but-2-ylcarbinyl cations

A synthesis for the unsubstituted bicyclo[1.1.0]but-2-ylmethanols (endo- and exo-9) from 1,3-butadiene has been developed. Solvolyses of their sulfonates 10 and 11 took entirely different courses, as the endo compound 10 gave rise exclusively to rearranged products such as cyclopent-3-en-1-ol (14), while the exo compound 11 underwent only the substitution of the tosylate group with complete retention of the exo-bicyclo[1.1.0]but-2-ylmethyl skeleton. Under solvolytic conditions, 10 reacted at very similar rates to the corresponding monocyclic substrate, that is, cyclopropylcarbinyl mesylate (19); in contrast, 11 reacted only three times as fast as n-butyl tosylate and about 1000-fold slower than 10. The nature of the bicyclo[1.1.0]but-2-ylcarbinyl cations has been probed by quantum chemical calculations. Whereas, the exo isomer (exo-18) corresponds to a local energy minimum, the endo isomer is only a transition state [endo-18(TS)] for an automerization of the nonclassical cyclopent-3-en-1-yl cation (13) and converts into 13 by a Wagner-Meerwein rearrangement. The most favorable isomerization of exo-18 also leads to 13 but via a transition state resembling the 2-vinylcycloprop-1-yl cation [25(TS)]. On the introduction of methyl groups at positions 1 and 3 of exo-18, the cation is no longer an energy minimum and it becomes a transition state [27(TS)] for an automerization of the nonclassical 1,3-dimethylcyclopent-3-en-1-yl cation (28). The large effect of the methyl substitution rationalizes the puzzling results of the previous product and rate studies, which utilized various substituted derivatives of bicyclo[1.1.0]but-2-ylcarbinyl sulfonates as substrates.     

Low temperature 13C NMR magnetic resonance in solids 4. Cyclopropane,bicyclo[1.1.0]butane and [1.1.1] propellane

The solid state ¹³C NMR spectra of bicyclo[1.1.0]butane and [1.1.1]propellane have been measured at low temperature. The orientation of the principal axes of the chemical shielding tensor have been determined with ab initio calculations based on the IGLO (Individual Gauge for Localized Orbitals) method when they are not determined by symmetry. Excellent agreement is obtained between the calculated and experimental principal values of the shielding tensor when basis sets containing polarization functions are used. In most cases the agreement is such that the calculated values are within the experimental error.Part 3 of this series: Ref. [7]     

Formal Alder-ene reaction of a bicyclo[1.1.0]butane in the synthesis of the tricyclic quaternary ammonium core of daphniglaucins

A tricyclic substructure of the tetracyclic nitrogen core of the daphniglaucins was formed by an oxidative activation of the allyl side chain of a bicyclo[1.1.0]butylmethylamine, a spontaneous intramolecular formal Alder-ene reaction, and a selective cyclization of a triol intermediate.