Asymmetric synthesis of 4-amino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans

✍ Scribed by Andreas Burgard; Hans-Jochen Lang; Uwe Gerlach

• Publisher: Elsevier Science
• Year: 1999
• Tongue: French
• Weight: 385 KB
• Volume: 55
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(99)00376-2

✦ Synopsis

Highly enantioselective reduction of 3,4-dihydro-2,2-dimethyl-2H-l-benzopyran-4-ones 3 s-e by BH3 was achieved in the presence of catalytic amounts of Corey's oxazaborolidine 4 to afford the corresponding 3,4-dihydro-2,2dimetbyl-2H-l-~nzopyran-4-ols 2a-e in quantitative yields. These benzopyran-4-ols 2a-e were converted into the chiral 4-amino-3,4-dihydro-2,2-dimethyl-2H-l-benzopyrans la-e by mesylation, followed by introduction of an azide group by tetra-n-butyl-ammonium azide, and finally by reduction of the azide 6 with triphenylphosphine under very mild conditions without loss of stereo information.