Asymmetric alkylation of aromatic aldehydes with dialkylzinc catalyzed by novel amino derivatives of hydroxytetrahydropyran

✍ Scribed by Günther Oehme; Irina Iovel; Edmunds Lukevics

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 56 KB
• Volume: 13
• Category: Article
• ISSN: 0268-2605
• DOI: 10.1002/(sici)1099-0739(199907)13:7<481::aid-aoc860>3.0.co;2-z

✦ Synopsis

Novel, specially prepared, tetrahydropyranbased g-amino alcohols (S)-2-(aminomethyl)-3-hydroxy-6-ethoxy(phenoxy)-tetrahydropyrans (I) (amino = n-Bu 2 N, piperidinyl, pyrrolidinyl, azetidinyl) were tested as catalysts in the asymmetric addition of Et 2 Zn and n-Bu 2 Zn to (hetero)aromatic aldehydes. In most cases the phenoxy derivatives of I acted more enantioselectively than the ethoxy ones. The dibutylamino derivaties showed the least enantioselectivity; the pyrrolidinyl derivatives were more active as catalysts than piperidinyl and azetidinyl compounds. The highest enantioselectivity was observed in the addition of Et 2 Zn to benzaldehyde in the presence of (S)-2-(N-pyrrolidinylmethyl)-3-hydroxy-6-phenoxytetrahydropyran. The corresponding alcohol was prepared with 72% ee (R-configuration). The addition of dibutylzinc proceeded slowly and less selectively. The alkylation of (hetero)aromatic aldehydes with Et 2 Zn and n-Bu 2 Zn was also studied in the presence of the known optical inductor (1S,2R)-N,N-dibutylnorephedrine. Some chiral aromatic secondary alcohols were synthesized in high chemical yields and up to 93% ee enantioselectivity.