| Abstract
| - A set of cycloisomerization methodologies of alkynyl ketones and imines with concurrent acyloxy,phosphatyloxy, or sulfonyloxy group migration, which allow for the efficient synthesis of multisubstitutedfurans and N-fused heterocycles, has been developed. Investigation of the reaction course by way ofemploying 17O-labeled substrates allowed for elucidation of the mechanisms behind these diversetransformations. It was found that, while the phosphatyloxy migration in conjugated alkynyl imines in theircycloisomerization to N-fused pyrroles proceeded via a [3,3]-sigmatropic rearrangement, the analogouscycloisomerization of skipped alkynyl ketones proceeds through two consecutive 1,2-migrations, resultingin an apparent 1,3-shift, followed by a subsequent 1,2-migration through competitive oxirenium anddioxolenylium pathways. Investigations of the 1,2-acyloxy migration of conjugated alkynyl ketones en routeto furans demonstrated the involvement of a dioxolenylium intermediate. The mechanism of cycloisomerization of skipped alkynyl ketones containing an acyloxy group was found to be catalyst dependent; Lewisand Brønsted acid catalysts caused an ionization/SN1‘ isomerization to the allene, followed by cycloisomerization to the furan, whereas transition metal catalysts evoked a Rautenstrauch-type mechanistic pathway.Furthermore, control experiments in the cycloisomerization of skipped alkynyl ketones under transition metalcatalysis revealed that, indeed, these reactions were catalyzed by transition metal complexes as opposedto Brønsted acids resulting from hydrolysis of these catalysts with eventual water. Further synthetic utilityof the obtained phosphatyloxy-substituted heterocycles was demonstrated through their efficient employmentin the Kumada cross-coupling reaction with various Grignard reagents.
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