Stereoselective reaction of arylsulfanyl-stabilized homoenolates with aldehydes

Highly Enantioselective Reactions of Configurationally Labile α-Thioorganolithiums Using Chiral Bis(oxazoline)s via Two Different Enantiodetermining Steps

“…A good level of enantioselectivity has been achieved in the reaction of nondipole-stabilized α-seleno carbanions through a dynamic thermodynamic resolution pathway . However, there have been no reports on the highly enantioselective reaction of nondipole stabilized α-sulfenyl carbanions . It is important to clarify the reaction pathways of α-sulfenyl carbanions and to develop highly enantioselective reactions.…”

Asymmetric Deprotonation with Alkyllithium–(−)‐Sparteine

“…Control experiments revealed that not only the rapid interconversion of 185 and epi-185 is the problem, but also the degree of stereodifferentiation in the deprotonation step is low 125 . The (−)-sparteine-mediated double deprotonation of 3-arylthio-N-methylpropanamides 187 to dilithiated arylsulphides 188, followed by aldehyde addition, also provided low, strongly varying enantiomeric excesses of the resulting products 189 (equation 43) 133 . …”

Stereoselectivity of Chiral Homoenolate Equivalents

“…3-Arylsulfanyl-substituted secondary amides 178 could also be dilithiated with 2.2 equivalents butyllithium in THF at Ð78¡C in the presence of (Ð)-sparteine. 108 With aromatic aldehydes anti-homoaldol adducts 179 were obtained with up to 96% de. However, only poor enantioselectivities were observed (Table 25), benzaldehyde and o-tolylcarbaldehyde exhibited almost the same diastereoselectivity, whereas aliphatic aldehydes exhibited opposite and lower diastereoselectivities.…”