An efficient chiral gold(I) complex-catalyzed synthetic method that enables the cycloisomerization/regio-and enantioselective nitroso-Diels−Alder (NDA) reaction of 1,6-diyne esters with nitrosobenzenes is described. The sequential ring formation protocol offers access to a wide variety of 3,5,6,8a-tetrahydro-1H-benzo[c][1,2]oxazines as a single regioisomer in yields up to 99% and enantiomeric excess values of up to 99%. This is in contrast to the analogous NDA reactions of the cycloisomerized 1,6-diyne ester with nitrosoarenes in the absence of the chiral gold(I) complex catalytic system, which were found to give the N,Oheterocyclic product with the opposite regiochemistry. Experimental and computational studies based on a postulated chiral dinuclear gold species containing two coordinated nitrosoarene molecules that undergoes an asynchronous concerted NDA reaction with the cycloisomerized 1,6-diyne ester provides insight into the observed product regio-and enantioselectivities.
A synthesis of indolo[3,2-c]quinolines and benzothieno[3,2-c]quinolines has been developed employing o-alkynyl-N-phenylformamide derivatives as the substrates. The reaction proceeded via a tandem process involving POCl3‒assisted intramolecular cyclization of the firstly formed...
A synthetic method for the preparation of 1,8-dihydroindeno[2,1-b]pyrroles and pyrrol-2-yl methanols in an enantioselective manner that relies on the chiral gold(I)-catalysed reactions of -amino-1,4-enynols is described. A divergence in product selectivity was achieved by exploiting the electrostatic interactions between the chiral counteranion of the metal catalyst and the substrate. With a gold(I) complex containing a chiral triflylamide-based counteranion, tandem dehydrative Nazarov-type electrocyclization/hydroamination of the substrate was found to selectively occur to afford the indeno-fused pyrrole adduct. In contrast, changing to a chiral phosphate-based counteranion was observed to result in a hydroamination/1,3-allylic alcohol isomerisation cascade pathway to give the 1H-pyrrole derivative.
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