Synthesis of new chiral hydroxy oxazolines and their use in the catalytic asymmetric phenyl transfer to aldehydes

Practical Implications of Boron‐to‐Zinc Transmetalation for the Catalytic Asymmetric Arylation of Aldehydes

“…A variety of aryl boron species have been used for this purpose, [5][6][7] as well as several other reagents. [8,9] In fact, a catalytic enantioselective aldehyde arylation involving a triaryl boroxine [10] as the ultimate source of the aryl group has recently found an industrial application.…”

“…In apparent contradiction to this prediction, however, standard experimental procedures for transmetalation normally involve heating a mixture of boroxine or boronic acid and a large excess of diethylzinc for extended periods of time (typically 12 h at 60 8C). [5,6] These problems can be partially overcome by using triaryl boroxines, although several hours are still necessary for the transfer the aryl moieties from boron to zinc, [7] which is a drawback of this methodology for practical applications.…”

Highly Regioselective Addition of Organozinc Reagents to 2‐Oxo‐1,2‐dihydropyrimidine‐5‐carboxylates Activated by BF3·OEt2: Synthesis of 2‐Oxo‐1,2,3,4‐tetrahydropyrimidine‐5‐carboxylates

“…Oxidation of 14 to 15 was also successfully achieved by us recently by using pyridinium chlorochromate (PCC) 22. The addition of freshly prepared organozinc reagents23,24 to 15a – d furnished exclusively the corresponding DHPM derivatives 16a – p substituted at C‐4 by an alkyl or phenyl substituent.…”

Triphenylboron

“…10 The main advantages of this approach are (1) that the boron-containing side product (triethylboron) can be easily removed under reduced pressure and (2) that the product diphenylzinc contains no metal salts (Mg or Li salts, especially). [13][14][15][16] Similarly, this mixture has proven effective for the transfer of a phenyl group to a N-diphenylphosphinoyl imine. 12 In this case, the use of triphenylboron was superior to all other tested phenyl-source reagents.…”