Enantioselective Synthesis of Ferrocene‐ or Cymantrene‐Fused Planar‐Chiral Phospholes

Abstract

Planar-chiral ferrocene-fused phosphole (S)-1a was prepared in an enantiomerically pure form by enantioselective transformation. The synthesis was started with Kagan's chiral ferrocenyl acetal (-)-2a, and bromo and (Z)-2-bromovinyl substituents were introduced at the 1-and 2-positions of the ferrocene platform in (S)-6a with controlling its planar chirality. The

Versatile and Enantioselective Preparation of Planar-Chiral Metallocene-Fused 4-Dialkylaminopyridines and Their Application in Asymmetric Organocatalysis

“…The first asymmetric reaction catalyzed by (S)-1 is an addition reaction of 2-t Bu-phenol (19) to ethyl(p-tolyl)ketene (18), which was suggested to take place by the Bro̷ nsted acidcatalyzed mechanism (Table 1). 9i The η 5 -C 5 Me 5 derivatives, (S)-1bw−bz, were prepared by our first-generation synthesis, and their catalytic applications in this reaction were already examined in the previous report.…”

“…An analogous synthetic strategy has been applied to the synthesis of metallocene-fused planarchiral phospholes recently. 18 Although the synthetic method in Scheme 2 provided a library of the planar-chiral pyridine-based nucleophilic organocatalysts, including previously unknown species, without chiral resolution, it still had room for further improvement. For example, the reaction sequence in Scheme 2 is somewhat lengthy and some steps require the use of expensive noble metal catalysts, such as the Hoveyda/Grubbs-II catalyst, 19 with relatively high catalyst loading.…”

“…Planar-chiral 4-pyridones 2 , obtained in essentially enantiomerically pure forms, are versatile synthetic intermediates, and they could be converted to the various pyridine derivatives with retention of the planar chirality in 2 . An analogous synthetic strategy has been applied to the synthesis of metallocene-fused planar-chiral phospholes recently …”

“…Enantioselective Addition of o-t Bu-Phenol (19) to Ethyl(p-tolyl)ketene(18) Catalyzed by (S)-1 a The reaction was carried out in toluene at 23 °C in the presence of catalyst (S)-1 (3 mol %). The absolute configuration of 20 was deduced by comparison with the reported results.…”

Alkyne Insertion into P–C(sp2) Bonds as a Route to Fused Phospholes: Transition-Metal-Like Reactivity at Phosphorus

“…Fused phospholes have applications as components for optoelectronic materials − and also have been used as ligands for catalytic applications. , As a result, synthetic routes to fused phospholes are of great interest. They are most commonly synthesized via metalation-cyclization ,,, or through transition-metal-catalyzed alkyne annulation reactions. − Other methods applied to their synthesis include Fagan–Nugent Ti mediated cyclization, rearrangement of phosphirenes, intramolecular CH activation by phosphinidene complexes, and photocatalyzed annulation reactions . The alkyne annulation reactions, whether metal-mediated or photocatalyzed, offer very efficient routes to benzophospholes; however, regioselectivity remains a challenge, with mixtures of direct and rearranged products resulting.…”