Halosulfonyl isocyanates

Many synthetic processes have been described for acesulfame. One involves the condensation of a halosulfonyl isocyanate and an acetylene or a ketone (67,68). The duorosulfonyl isocyanate can be prepared by reaction of sulfuryl diisocyanate with duorosulfonic acid (69). 

The difference in reactivity of halosulfonyl isocyanates is shown in equation 84. The reaction of 146 with 2-butyne gave the [2 + 2]adduct in moderate yield, which was hydrolyzed to 163 by treatment with methanol. In contrast, 2 equivalents of fluorosulfonyl isocyanate reacted with 2-butyne to give a six-membered heterocycle, which on hydrolysis rearranged to 16279. 

In the reaction of acetylenes with halosulfonyl isocyanates (X = F,C1) 6-halo-l,2,3-oxathiazine-2,2-dioxides 57 are obtained. Rearrangement of the initial [2+2] cycloadduct to an imino ketene, followed by cyclization, accounts for the formation of 57. With two... 

In Table 3.5 some of the [2+2] cycloadducts 64 derived from halosulfonyl isocyanates and linear olefins are listed. Review articles on the chemisfiy of chlorosulfonyl isocyanate appeared in 1976 and in 1986. ... 

Table 3.5 Some [2+2] cycloadducts of halosulfonyl isocyanates and linear olefins...

Also, it is of importance to remove acidic impurities from the halosulfonyl isocyanates because they cause isomerization of the cycloadducts or rearrangement. Therefore, the reactions should be performed in the presence of sodium, potassium or calcium carbonate. 

The reactivity of isocyanates in [2+2] cycloaddition reactions is as follows alkyl < aryl < nitroaryl << arenesulfonyl < halosulfonyl. Also, the reactivity of the substrate is determined by the substituents. For example, vinyl ethers and enamines are more reactive than olefins. Often the formation of the [2+2] cycloadducts involves polar linear intermediates, which can be intercepted by the isocyanate or the substrate to form six-membered ring [2+2+2] cycloadducts (see Section 3.3.1.4). Also, diynes react with isocyanates to give six-membered ring [2+2+2] cycloadducts. In the latter reactions catalysts play an important role. From Q, ty-diynes macrocyclic adducts are obtained. 

In the [2+2] cycloaddition reaction of thioketenes with chloro- and fluorosulfonyl isocyanates the [2+2] cycloadducts are not isolated, but j8-thiolactams resulting from the hydrolysis of the halosulfonyl groups are obtained. 

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