Conformationally isomeric carbonium ions in condensed ring systems

Abstract

15 min at 85°. Distillation gave dimethylphenyldifiuorophos-phorane25•26 (10) in 91% yield. This substance had bp 30°( 0.02 mm). The nmr spectrum of a fresh solution in CDC13 at 25°h ad six protons at 8.20 ppm, /m> = 17.7 cps, /hf = 12.5 cps (doublet of triplets), and five aromatic protons. For (C6H5)-(CH3)2P: t 8.75 ppm, /up = 2.7 cps. See 31P nmr data in the Results section.The residue from the above distillation solidified and was characterized as (C6FFP)S ( 12), mp 150-155=, 31 = +4.3 ppm; the material was isolated in 85 % yield.(b) An equimolar mixture of dimethylphenylphosphine and difluorophenylphosphine was kept 5 min at 20°. The mixture was dissolved in CH2C12 and the solution was analyzed by 31P nmr spectrometry. It contained unreacted tertiary phosphine and fluorophosphine and relatively small amounts of the phosphorane, 10, and (C6HaP)3,12, but no other intermediates or by-products.Reaction with Methyldiphenylphosphine. Equimolar amounts of the reagents were kept 15 min at 20°. No reaction was detected. Reaction was complete after 7 days at 20c. The products were methyldiphenyldifluorophosphorane25'26 (11) and (CeFEP).-, (12).

Nucleophilic Reactions at Tertiary Carbon. Part 3. σ‐ and π‐routes to the 9‐decalyl cation

“…On the basis of product analyses Gream suggested that ion pairs 3 involving cis-and tram-like conformers of the decalyl cation are involved and that the counter ion plays an important role in product formation. This viewpoint contrasts with that of Fort [4] but is in general agreement with our previous tentative interpretation [l] …”

“…Furthermore, no evidence for conformationally isomeric cations, as suggested earlier [l] and as claimed by Fort [4], was found, nor for ion pairs involving cis-and trans-like conformers of the decalyl cation, as suggested by Gream [7].…”

“…To summarize the results of our study of the 1, 2-dimethylcyclohexyl, the hydrindanyl and the decalyl systems, the cationic intermediates generated by different routes are satisfactorily describcd as stereoisomeric ion pairs and unsymmetrically solvated cations. Furthermore, no evidence for conformationally isomeric cations, as suggested earlier [l] and as claimed by Fort [4], was found, nor for ion pairs involving cis-and trans-like conformers of the decalyl cation, as suggested by Gream [7].…”

“…[4] who solvolyzed the corresponding $-nitrobenzoates cis-and trans-lb in 60% acetone. These authors also studied the rate and products of cis-and trans-8-hydrindanyl $-nitrobenzoate (4b) and the corresponding derivatives of bicyclo [3.3.0]octane, i.e.…”

“…This is also the case with the corresponding chlorides, which are only isomerized in the presence of catalysts, as shown above. However, failure to detect ion pair return in nucleophilic solvents, such as aqueous ethanol and acetone, does not exclude their intermediacy, especially if reaction of the cations with solvent is a diffusion-controlled process, as assumed by Fort [4]. There is therefore no reason to disregard the fundamental role of ion pairs and selective solvation in controlling reactions at tertiary carbon.…”