An Approach to Enantioselective 5‐endo Halo‐Lactonization Reactions

Abstract

Enantioselective lactonization of 4‐substituted but‐3‐enoic acids using iodobis(N‐methylephedrine) hexafluoroantimonate in dichloromethane at low temperatures is reported. The presence of bis(N‐methylephedrine)silver(I) hexafluoroantimonate, derived from the excess amounts of N‐methylephedrine and silver hexafluoroantimonate that were necessary for the generation of the iodo complex in the reaction mixture, is crucial for the success of this reaction. The different parameters of these cyclization reactions have been examined. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Toward Catalytic, Enantioselective Chlorolactonization of 1,2-Disubstituted Styrenyl Carboxylic Acids

“…In 1992, Taguchi and co-workers reported the first enantioselective halolactonization, promoted by stoichiometric amounts of chiral titanium complex, affording enantioenriched iodo lactones in 65% ee. 14 A number of other methods employing stoichiometric reagents such as chiral amines, 15 pyridines, 16 and dimeric iodonium salts 17 have been reported.…”

Achiral Counterion Control of Enantioselectivity in a Brønsted Acid-Catalyzed Iodolactonization

“…alkene iodoacyloxylation outlined in Figure 2) were possible while careful mechanistic studies 2,3,4 outlined obstacles to significant, if not practically meaningful, enantioselectivity. 5,6,7 Within the broader topic of alkene halofunctionalization, the earliest strategies centered on Lewis base-promoted halogenation strategies, such as chiral amine 8,9 and phosphoramidite 10 methods for halolactonization and polyene cyclization, respectively. A strategically complementary strategy involves Lewis acid activation of the halogen donor: haloamination of a chalcone alkene, 11 and enolsilane chlorination.…”

Facile Oxidative Rearrangements Using Hypervalent Iodine Reagents

“…Furthermore, phenyl and methyl group-bearing substrates ( E )- 1 f and ( Z )- 1 f were prepared. Compound ( E )- 1 f was photochemically isomerized to ( Z )- 1 f 11. Acid ( E )- 1 f was rearranged to compound 2 f in 89 % yield (Table 2, Entry 6), whereas ( Z )- 1 f exclusively formed the cyclization product 4 f in 81 % yield without rearrangement (Table 2, Entry 7).…”