Yang cyclization enantioselectivity

Some structures of this type of compound were established by X-ray diffraction analysis. For example, the structure of compound 84 resulting from the enantioselective Norrish-Yang cyclization of prochiral imidazolidinone was... 

Yang described the Pd-induced cyclization of an aryl bromide onto a pendant cyano group leading to y-carbolines and related compounds [488], Genet studied the use of chiral palladium complexes in the construction of the C-ring of ergot alkaloids, a study that culminated in a synthesis of (-)-chanoclavine I [489-491]. For example, nitroindole 388 is cyclized to 389 in 57% yield and with enantioselectivities of up to 95% using Pd(OAc)2 and (S)-(-)-BINAP. 

Highly enantioselective atom transfer radical cydization reactions catalyzed by chiral Lewis acids have been reported by Yang et al. [80]. Two main advantages of these enantioselective cyclizations include installing multiple chiral centers and retaining a halogen atom in the product, which allows for further functionalization. 

In their enantioselective total synthesis of (+)-triptocallol (3-79), a naturally occurring terpenoid, Yang and coworkers made use of a concise Mn(OAc)rmediated and chiral auxiliary-assisted oxidative free-radical cyclization [39]. Reaction of 3-77, bearing a (R)-pulegone-based chiral auxiliary, with Mn(OAc)3 and Yb(OTf)3 yielded tricyclic 3-78 in a twofold ring closure in 60% yield and a diastereomeric ratio of 9.2 1 (Scheme 3.20). A further two steps led to (-i-)-triptocallol (3-79). For the interpretation of the stereochemical outcome, the authors proposed the hypothetical transition state TS-3-80, in which chelation of the (3-keto ester moiety with Yb(OTf)3 locks the two carbonyl groups in a syn orientation. The attack of the Mn -oxidation-generated radical onto the proximate double bond is then restricted to the more accessible (si)-face, as the (re)-face is effectively shielded by the 8-naphthyl moiety. 

In 2014, Yang and Yoshikai reported enantioselective intramolecular hydroacylation reactions of ketones and olefins using cobalt-chiral diphosphine catalysts (Scheme 10.7) [21]. A cobalt catalyst generated by the reduction of CoBr2 with indium powder in the presence of l,2-bis((2R,5R)-2,5-diphenylphospholano)ethane ((R,R)-Ph-BPE) promotes cyclization of a variety of 2-acylbenzaldehydes to afford phthalide derivatives in moderate... 

An enantioselective version of the similar type of cyclization strategy has been developed by Yang et al., where they used properly designed substituted aniline derivatives in the presence of catalytic Pd(trifluoroacetic acid [TFA])2 and chiral (—)-sparteine ligand to afford... 

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