Some aspects of the chemistry of chlorosulphonyl isocyanate.

The reactions of chlorosulphonyl isocyanate with cyclic 1, 3-dienes gave thermally unstable N-chlorosulphonyl B-lactams which were intercepted by reduction to the corresponding stable NH-B-lactams. The exclusively Markovnikov orientation of the addition suggests a considerable degree of dipolar character in the transition state. Stepwise rearrangement of the initial 1, 2-addition products to thermodynamically more stable 1, 4-addition or substitution products was observed and the assignment of these products is discussed. The invertomer ratios and activation energies for inversion at nitrogen in several 2-chloro-2-zabicyclo [2, 2, 17] and [2, 2, 2] systems, derived from rearrangement products obtained in the reactions of chlorosulphonyl isocyanate with 1, 3-cyclopentadiene and 1, 3-cyclohexadiene, were determined using variable temperature n.m.r. spectroscopy. The assignment of the invertomers, and factors influencing the invertomer ratio and activation energy for inversion at nitrogen in bicyclic systems are discussed. The reaction of chlorosulphonyl isocyanate with vinylcyclopropanes also gave unstable Markovnikov orientated N-chlorosulphonyl B-lactams which were readily reduced to the corresponding stable NH-B-lactams. Rearrangement of the initial 1, 2-addition products occured, in general, via proton transfer to yield N-chlorosulphonyl amides with retention of the cyclopropyl ring. A rearrangement involving the cyclopropyl ring, to give an N-chlorosulphonyl azepinone, was only observed under certain conditions in the case of [special character omitted]-cyclopropylstyrene The kinetics of the reactions of chlorosulphonyl isocyanate with vinylcyclopropanes were investigated using i.r. spectroscopy; the effects of solvent polarity and substituents on the reaction rate were consistent with an initial dipolar addition. The unexpectedly low reactivity and magnitude of the Hammett reaction constant found for [special character omitted]-cyclopropylstyrenes, was explained in terms of steric inhibition of resonance in the dipolar intermediate. The reactions of chlorosulphonyl isocyanate with epoxides, yielding, in general, N-chlorosulphonyl-1, 3-oxazolidin-2-ones and N-chlorosulphonyl- 2-imino-l, 3-dioxolans, were investigated. The assignment of the products is discussed and a dipolar addition mechanism is proposed. This mechanism is supported by the isolation of proton transfer products in the reactions of cyclo-octatetraene epoxide and terpene oxides, and the influence of the structure of the dipolar intermediate on the course of the reaction is discussed.