Cycloaddition of sulfonyl isocyanates

Some intramolecular [2+2] cycloadditions of sulfonyl isocyanate-olefins have been studied by Metz et al. [116]. These authors found that the intramolecular reaction depicted in Scheme 36 was calculated to be endergonic at the B3LYP/6-31G and B3LYP(PCM)/6-31G levels, the corresponding free activation energies being in the... 

Effenberger, F, Kiefer, G, Stereochemistry of the cycloaddition of sulfonyl isocyanates and A-sulfinylsulfonamides to enol ethers, Angew. Chem. Int. Ed., 6, 951-952, 1967. 

Stereochemistry, substituent effects and activation parameters of most ketene reactions are consistent with a one-step cycloaddition polar effects of substituents and solvents, as well as the isotope effect, often require, however, that a fair amount of charge separation (that is, unequal bond formation) characterises the transition state. It has been kinetically proved that cycloadditions of enamines to ketenes can also proceed through a dipolar intermediate this is so for the reaction between dimethylketene and N-isobutenylpyrrolidine . In the latter case, the rate coefficient for the formation of the intermediate strongly depends on solvent polarity itacetonuriie/ cyclohexane = 560. Use of the Same criteria used for ketenes (as far as experimental data allow it) in the case of the 1,2-cycloadditions of fluorinated olefins results, instead, in the conclusion that a two-step biradical mechanism is operating. Results for 1,2-cycloaddition of sulfonyl isocyanates to olefins, cases (g) and (h) in Table 17, give indications of dipolar intermediates during the course of these reactions. 

---

See also in sourсe #XX -- [ ]

---