Chlorosulphonyl isocyanate, cycloaddition

Cycloadditions of electrophilic olefins or cumulenes to vinylcyclopropanes should also be mentioned in this context, since in most cases stepwise reactions starting with an electrophilic attack are very likely. One example operating with chlorosulphonyl isocyanate and providing a seven-membered lactam is depicted in equation 152 however, so far most reactions in this area have a limited synthetic potential. 

Sulfonyl isocyanates seem able to undergo stereospecific or highly stereoselective reactions. The cycloadditions of chlorosulphonyl isocyanate to cis and trans isomers of /3-methylstyrene and of 3-hexene were carried with retention of the olefin configuration . The initial products of the following reaction (R = p-MeCgH4S02-)... 

Fowler, F. W. Cycloadditions of N-methoxycarbonyl-2,3-homopyrrole . Angew. Chem. 1971, 83, 148-149. Angew. Chem. Int. Ed. Engl. 1971,10, 135-136. Baldwin, J., Pinschmidt, R. K. jr. The Cycloaddition of Bicyclo2.1.0pent-2-ene with Tetracyanoethylene . Tetrahedron Lett. 1971, 935-938. Christl, M., Brunn und E., Lanzendoerfer, F. Reactions of Benzvalene with Tetracyanoethylene,2,3-Dichloro-5,6-dicyano-p-benzoquinone, Chlorosulphonyl Isocyanate, and Sulphur Dioxide. Evidence for Concerted 1,4-Cycloadditions to a Vinylcyclopropane System . J. Am. Chem. Soc. 1984,106, 373-382. 

Neooctams, such as the unsubstituted parent compound (191), are easily obtained in cycloadditions. Isocyanates [125,126], sulphonyl isocyanates (43) [29,127] and especially chlorosulphonyl isocyanate (189) [128] react with alkenes to form variously-substituted j3-lactams [129—135]. Synthesis of compound (191) is an example of this reaction which has been discussed in detail [52]. The same compound (192) can be obtained in the photolytic rearrangement of the pyrazolone (194) [136]. Compound (196) is neooctam-5,7-diene, obtained from the azocine (195) and hydrogen bromide [137]. Lactam (196)is a partly saturated form of (199). The latter is an unstable neooctam derivative, formed in an intramolecular ketene-imine cycloaddition reaction (see (198))... 

Further details have been published of the cycloadditions of alkenylidenecyclo-propanes with 1-phenyl-1,3,5-triazoline-2,5-dione, which were discussed in detail in an earlier Report. The stereospecificity observed with chiral alkenylidenecyclo-propanes supports the proposal of a cycloaddition pathway involving an eight-electron (i.e. Mobius) transition state, [( +, 2 -I- 2) -I-, 2]. Partial or complete loss of stereochemistry, depending on temperature, is observed with chlorosulphonyl isocyanate, implying a dipolar intermediate, and l,l-dichloro-2,2-difluoroethylene appears to add via biradicals. ... 

Cyclohexenes and Cyclohexadienes. The stereochemistry of cycloadditions to methyl-enecyclohexanes has been a somewhat neglected area. Recently, the addition of dichloroketen and chlorosulphonyl isocyanate to methylenecyclohexane and 4-t-butylmethylenecyclohexane has been studied as models for a 2s + 2a allowed cycloaddition. The reaction is kinetically controlled and axial attack dominates, yielding the thermodynamically less stable isomer (as confirmed by a molecular mechanics calculation). There is complete regiospecificity due to the polar character of the transition state. 

We discuss here a number of cycloadditions, which probably proceed via polar intermediates. Reactions are described in Scheme 15. The additions of chlorosulphonyl isocyanate indicate the possibility of reversible formation of a kinetic adduct [e.g. (54)] which via a dipolar species can equilibrate to a thermodynamic adduct [e.g. (55)]. The precise nature of a product depends upon solvent, reaction time, and temperature, but by suitable choice of conditions high yields are possible. Various transformation products of (56), available in low yields, are described and the further transformation of (56) into (57) is noted. In contrast to V-nitrosoaziridines, (57) is thermally stable. 

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