Efficient pi-facial control in the ene reaction of nitrosoarene, triazolinedione, and singlet oxygen with tiglic amides of the bornane-derived sultam as chiral auxiliary: an economical synthesis of enantiomerically pure nitrogen- and oxygen-functionalized acrylic acid derivatives.
The ene reaction of 4-nitronitrosobenzene (ArNO), N-phenyl-1,2,4-triazoline-3,5-dione (PTAD), and singlet oxygen (1O2) with the optically active tiglic-acid derivatives of Oppolzer's bornane-derived sultam affords the respective ene products regioselectively in excellent diastereoselectivity (de up to 99%) and in good yield (55-90%). The enophiles ArNO and PTAD give with the methyl-substituted substrate exclusively the like-configured ene adduct, while 1O2 leads to an 83:17 diastereomeric mixture. With the sterically more demanding isopropyl-substituted derivative even the smallest enophile 1O2 forms exclusively the like diastereomer. The high diastereoselectivity is rationalized in terms of the proper conformational alignment of the substrate and a preferred enophilic attack from the C(beta)-re face of the double bond. This concept offers an efficient synthetic route to enantiomerically pure nitrogen- and oxygen-functionalized acrylic acid derivatives.
Adam
Waldemar
W
Institut für Organische Chemie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. adam@chemie.uni-wuerzberg.de
Degen
Hans-Georg
HG
Krebs
Oliver
O
Saha-Möller
Chantu R
CR
D000179:Acrylates / Q000138:chemical synthesis* / Q000737:chemistry; D000475:Alkenes / Q000737:chemistry*; D000596:Amino Acids / Q000138:chemical synthesis*; D001892:Camphanes / Q000737:chemistry*; D009603:Nitroso Compounds / Q000737:chemistry*; D026082:Singlet Oxygen / Q000737:chemistry*; D013237:Stereoisomerism; D014230:Triazoles / Q000737:chemistry*
D000179:Acrylates; D000475:Alkenes; D000596:Amino Acids; D001892:Camphanes; D009603:Nitroso Compounds; D014230:Triazoles; D026082:Singlet Oxygen