Enantioselective halolactonization

New catalytic approaches towards the enantioselective halolactonization of alkenes 12CA(456. 

Tan CK, Zhou L, Yeung Y-Y. Organocatal3dic enantioselective halolactonizations strategies of halogen activation. Syn-/ett 2011 10 1335-1339. 

Another enantioselective halolactonization to produce y-lactones (13) employs NIS in combination with the chiral Brpnsted acid catalyst (14) that is used at low loadings (>1 mol%). The reaction has been shown to be modulated by the counteranion and best results were obtained with NTfj. ... 

Catalytic, enantioselective halolactonization of (Z)-l,3-enynes (39) and 1,1-disubstituted alkenes with NBS has been reported to occur in the presence of chiral urea derivatives, such as (41), to produce allene derivatives (40) in <91% ee ... 

Although the field of organocatalysis has flourished over the past decade, there are still some areas that remain virtually untouched, such as the asymmetric a-halogenation of olefins. Several enantioselective halolactonization reactions of exocydic carboxylic acids have been reported since 2010 [41]. Borhan and coworkers reported the first highly enantioselective chlorolactonization of alkenoic acids... 

Intramolecular cyclization of unsaturated carboxylic acid derivatives using strong electrophiles is one of the most effective and common approaches to y-lactones. Not to mention, reactions of the unsaturated carboxylic acids with halonium sources such as X2 and NXS, the so-called halolactonization, produce the synthetically useful halolactones [4], N-Halosuccinimide (NXS) reaction is also commonly utilized for the construction of y-lactone structures. These days, development of effective catalysts, especially for enantioselective cyclization of unsaturated carboxylic acids including halolactonization reaction, is a hot topic in synthetic organic chemistry. 

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