Highly Substituted Furo[3,4‐d][1,2]oxazines: Gold‐Catalyzed Regiospecific and Diastereoselective 1,3‐Dipolar Cycloaddition of 2‐(1‐Alkynyl)‐2‐alken‐1‐ones with Nitrones

Gold(I)-catalyzed enantioselective cycloaddition reactions

“…The reactions provide fused heterobicyclic oxazine derivatives of type 27 with good yields and excellent regio- and diastereoselectivities. The racemic series, promoted by Ph 3 PAuCl/AgOTf as a catalyst [84], was translated into an enantioselective version by using any of the chiral bisgold complexes derived from ( R )-C1-Tunephos ( Au19 ) or ( R )-MeO-DTBM-Biphep ( Au5 ) (Scheme 17) [85]. From a mechanistic point of view, the authors proposed the generation of a zwitterionic furanylgold complex of type XIII by a gold-promoted intramolecular cyclization process.…”

Recent developments in gold-catalyzed cycloaddition reactions

“…In 2009, J. Zhang reported a gold(I)-catalyzed tandem cyclization/(3 + 3) cycloaddition of related 2-(1-alkynyl)-2-alken-1-ones 10 with nitrones [47]. The reactions provided a very practical entry to bicyclic oxazine derivatives 11 , which were obtained in good yields and excellent selectivities (Scheme 5).…”

Carbo- and heterocyclisation of oxygen- and nitrogen-containing electrophiles by platinum, gold, silver and copper species

“…Zhang et al 41 showed a gold-catalysed 1,3-dipolar cycloaddition of 2-(1-alkynyl)-2-alkene-1-ones 41-1 with nitrones, which provides a practical and highly diastereoselective route to heterobicyclic furo[3,4-d]-[1,2]-oxazines 41-2, as depicted in Scheme 41. This cyclisation proceeds via attack of the ketone at the p-alkyne moiety to give gold-containing furanyl cation 41a, which reacts with nitrone to deliver the observed [3 + 2]-cycloadducts…”