Keto alkyne cyclisation has been used to prepare tetrahydrobenzo [b] furans (4) and (15) but cyclopenta[b]furans are not available by this procedure. Compound (15) has been converted into benzofuran prostacyclin analogues (5) and (6) by extremely short routes. Conditions are also described for the conversion of the same keto alkynes into tetrahydrobenzo[b]- and cyclopenta[b]- thiophenes and -pyrroles, (7a,b) and (9a,b). Syntheses of thiophene prostacyclin analogues (8a) and (8b) are also discussed.
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Cook et al. (1987) studied this question.
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