Ring closing metathesis enyne precursors

Metal-mediated cyclizations have been applied to piperidine synthesis (Scheme 16). Ring closing metathesis catalyzed by Ru catalysts is used to prepare chiral piperidines <97TL677, 97AG(E)3036>. Similarly to the cyclization to 37 is Ti-(II)-mediated intramolecular cyclization of optically active enyne precursors for preparing chiral piperidines <97TL8351>. 

Nunez-Zarur F, Solans-Monfort X, Pleixats R, Rodnguez-Santiago L, Sodupe M. DPT Study on the Recovery of Hoveyda-Grubbs-Type Catalyst Precursors in Enyne and Diene Ring-Closing Metathesis. Chem Eur J. 2013 19(43) 14553-14565. 

Ring-Closing Metathesis of Enyne Precursor The first example of target-directed synthesis using enyne metathesis is the total synthesis of (—)-stemoamide 179, an alkaloid isolated from the roots of Stemona... 

Bicyclic dienic products recently synthesized by this method (Scheme 36) are lactams 144a and b (07T8267) and enamine ester 145 (09CEJ4565). The precursor of the latter substance originates from a four-component synthesis followed by y-allylation. The alternative y-propargylation and subsequent ring-closing enyne metathesis performed under an ethene atmosphere lead to the 8-vinyl derivative of product 145. 

By use of Ru-based carbenes such as [Ru]-Ia, II, III, various carbo- and heterocycles can be synthesized from the corresponding enyne precursors. The metathesis is carried out not only by ring-closing enyne metathesis but also by dienyne metathesis, cross enyne metathesis, and ring-opening enyne metathesis.In this section, the synthetic applications of enyne metathesis reactions, including skeletal reorganization reactions and hetero-enyne metathesis, to natural products and related compounds are described. 

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