238746-40-2Relevant academic research and scientific papers
Chiral auxiliaries for asymmetric radical cyclization reactions: application to the enantioselective synthesis of (+)-triptocallol.
Yang,Xu,Bian
, p. 111 - 114 (2007/10/03)
[figure: see text] A series of epimeric 8-aryl menthyl derivatives 5a-d and 6a-l, prepared from the same chiral source (R)-pulegone, were employed as chiral auxiliaries in the asymmetric radical cyclization reactions of beta-keto esters mediated by Mn(OAc)3. Chiral precursors 8c and 8d provided the cyclization products 10c and 10d, respectively, as single isomers (dr > 99:1), whereas the cyclization of precursor 9k gave 13k with good stereoselectivity (dr = 24:1). Diastereomer 13e was employed as the key intermediate in the enantioselective synthesis of (+)-triptocallol in 90% ee.
Enantioselective Total Synthesis of (-)-Triptolide, (-)-Triptonide, (+)-Triptophenolide, and (+)-Triptoquinonide
Yang, Dan,Ye, Xiang-Yang,Xu, Ming
, p. 2208 - 2217 (2007/10/03)
The first enantioselective total synthesis of (-)-triptolide (1), (-)-triptonide (2), (+)-triptophenolide (3), and (+)-triptoquinonide (4) was completed. The key step involves lanthanide triflate-catalyzed oxidative radical cyclization of (+)-8-phenylmenthyl ester 30 mediated by Mn(OAc)9, providing intermediate 31 with good chemical yield (77%) and excellent diastereoselectivity (dr 38:1). (+)-Triptophenolide methyl ether (5) was then prepared in >99% enantiomeric excess (>99% ee), and readily converted to natural products 1-4. In addition, transition state models were proposed to explain the opposite chiral induction observed in the oxidative radical cyclization reactions of chiral β-keto esters 17 (without an α-substituent) and 17a (with an α-chloro substituent).
