New chiral iodooxazoline catalysts for the I(III)-mediated α-tosyloxylation of ketones: refining the stereoinduction model
摘要:
A new family of iodooxazoline catalysts, derived from widely available chiral ketones (menthone and camphor), was developed to promote the iodine(III)-mediated alpha-tosyloxylation of ketone derivatives. The reaction conditions to achieve the direct formation of the oxazoline moieties from the corresponding aminoalcohols and an aldehyde were explored and optimized. These catalysts were tested for the alpha-tosyloxylation of propiophenone and led to new information on the stereoinduction process. The results demonstrate that modulation of the steric hindrance around the iodane center is critical to obtain good activity. Additionally, from the selectivities observed, a preliminary predictive model is proposed. (C) 2013 Elsevier Ltd. All rights reserved.
The addition of Me3SiCN and LICH2CN to (+)-camphor and (-)-fenchone. respectively, followed by reduction leads to chiral beta- and gamma -aminoalcohols. The enantioselectivities realized using these aminoalcohols as ligands in the addition of Et2Zn to benzaldehyde were lower than those obtained using the corresponding delta -aminoalcohols. (C) 2001 Elsevier Science Ltd. All rights reserved.