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A general route to the title compounds has been developed. This involves cyclisation of 2,3-dihydro-3-ureidothiophen SS-dioxides (20) with base. Both symmetrically and unsymmetrically substituted cis-fused ureas (2) can be prepared. A similar base-induced reaction of the corresponding 3-carbamoyl-2,3-dihydrothiophen SS-dioxides led, via the corresponding cyclic carbamates (8), by a route involving elimination and double-bond migration, to the corresponding 4-amino-2,3-dihydrothiophen SS-dioxides (11).
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Ellis et al. (1972) studied this question.
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