Iron(III)‐BPsalan Complex Catalyzed Highly Enantioselective Dearomative Chlorination of 2‐Hydroxy‐1‐naphthoates

Abstract

A practical, efficient Fe(III)‐BPsalan complex catalyzed asymmetric dearomative chlorination reaction of 2‐hydroxy‐1‐naphthoates derivatives (22 examples) was developed. With readily available Fe(III)‐BPsalan complex as catalyst at 5 mol% catalyst loading, various 2‐hydroxy‐1‐naphthoates derivatives bearing different substituents were efficiently chlorinated to afford chiral naphthalenones bearing a Cl‐containing all‐substituted stereocenter in high yields and with good to excellent enantioselectivities under mild reaction conditions. The reaction could be conducted at gram scale with the high efficiency and selectivity retained. In addition, the reaction could be extended to asymmetric dearomative bromination to afford the corresponding brominated product in 87% yield and 76% ee.

Fe-BPsalan Complex-Catalyzed Asymmetric [4 + 2] Cycloaddition of Cyclopentadiene with α,β-Unsaturated Heterocycles

“…AgBF 4 led to the best result in terms of yield, selectivity, and reaction time (Table , entry 5), while silver salts bearing a coordinative counteranion, such as AgNO 3 and AgOAc, were unable to promote the formation of the desired 3a (Table , entries 7–8). The higher activity of the iron catalysts upon the addition of noncoordinating silver salts may be attributed to the stronger Lewis acidic nature of the corresponding cationic iron complex and is consistent with our previous finding. − We subsequently employed various Fe-BPsalan complexes, 2b – 2h , bearing different substituents to catalyze the addition reaction with the additive, AgBF 4 (Table , entries 9–15). All iron complexes evaluated efficiently promoted the cycloaddition reaction to afford 3a in good results, albeit with a longer reaction time or lower yields and selectivity compared to that of 2a .…”

“…12 We have recently developed a series of Fe-BPsalan complexes supported by chiral tetradentate BPsalan N 2 O 2 ligands bearing a rigid chiral bipyrrolidine backbone, which may serve as powerful Lewis acid catalysts to promote asymmetric fluorination, 13 oxygenation, 13 and chlorination. 14 Most notably, these complexes exhibit remarkable performance in catalyzing the asymmetric Diels−Alder reaction of various alkylidene β-ketoesters with dienes to afford biologically important estrone analogues with high efficiency and selectivities via a cis type two point binding activation mode. 15,16 As the coordination mode of the reaction intermediate is essential in Fe-BPsalanpromoted asymmetric catalysis, we hypothesized that the absolute structure of the addition products in Fe-BPsalan complex-catalyzed Diels−Alder could be controlled by tuning the coordination mode.…”