Phosphoric acids, enantioselection rearrangement

The same catalyst has been used by this research group in synthesis of j -amino-aldehydes (146) by combining two catalytic reactions, i.e. a Ni(II) complex-catalyzed isomerization of a double bond and a chiral phosphoric acid (127)-catalyzed aza-Petasis-Ferrier rearrangement in a highly dia-stereo- and enantioselective manner (Scheme 39). ... 

Aminoindole 166 was found to undergo a catalytic, enantioselective aza-Claisen rearrangement upon heating in toluene with chiral phosphoric acid 168 to afford 2,3-disubstituted indole 167. A variety of substituents were competent under the reaction conditions and both yields and ee s were excellent in most examples. It was proposed that the rearrangement was accelerated and transferred high enantioselectivity by an arene CH—O interaction between the C2 proton and the phosphate counterion of 168 (13JA16380). 

An enantioselective semipinacol rearrangement has been reported. For example, the cyclobutanol derivative (184) reacts with an iodonium source (186) to provide the rearrangement product (185) in good yield (Scheme 39). In the presence of a chiral phosphoric acid, good chrial induction is obtained in product formation. The key steps in this conversion involve facial selectivity of iodonium attack and stereocontrol of the Wagner-Meerwein rearrangement step (187). Both steps are thought to be controlled by the chiral counterion. 

Korenaga and co-workers reported the precise mechanism of the highly anti- and enantioselective aza-Petasis-Ferrier (APF) rearrangement of hemiaminal vinyl ethers (254) catalysed by a chiral phosphoric acid (265) which has been investigated by both experimental and theoretical studies (Scheme 71). ... 

In 2009, the catalytic enantioselective semipinacol rearrangement of 2-oxo allylic alcohols 83 was detailed by Zhang et al., leading to enantioenriched spiro-ethers 84 in a single operation (Scheme 2.24). They found that both phosphoric acids 5b and silver phosphate 5i were optimal catalysts, while the latter probably underwent silver-proton exchange with hydroxyl group of subsnates in the catalytic procedure [35],... 

Subsequently, the same group demonstrated an asymmetric synthesis of 3-amino aldehydes via catalytic double-bond isomerization/enantioselective aza-Petasis-Ferrier rearrangement reaction (Scheme 2.93) [128]. Similarly, the hemiaminal allyl ether substrates 346 were first isomerized by Ni(II) complexes to stereoselectively form Z-configured vinyl ethers 347, which then underwent a phosphoric acid-catalyzed... 

Scheme 40.51 Phosphoric acid diester-catalyzed enantioselective semipinacol rearrangement of 2-oxo-allylic alcohols.

More recently, several approaches to catalytic, enantioselective Nazarov cyclizations have been developed [28]. Trauner reported that substrate 266 underwent electrocyclic rearrangement, furnishing 268 in 94 % ee in the presence of the chiral Sc-PYBOX catalyst 267 (Equation 30) [134]. The enantio-discriminating step in this cyclization is believed to be protonation of the intermediate enolate that ensues from the Nazarov cyclization. Rueping has documented enantioselective cyclizations of related dienones in the presence of the chiral phosphoric acid derivative 270 (Equation 31) [135]. Chiral Bronsted acid catalysis thus effected the cyclization of 269 to give products 271 (87% ee) and 272 (95% ee). 

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