134870-62-5Relevant articles and documents
Microwave-assisted synthesis of the Sch?llkopf chiral auxiliaries: (3S)- and (3R)-3,6-dihydro-2,5-diethoxy-3-isopropyl-pyrazine
Carlsson, Anna-Carin,Jam, Fariba,Tullberg, Marcus,Pilotti, ?ke,Ioannidis, Panos,Luthman, Kristina,Gr?tli, Morten
, p. 5199 - 5201 (2007/10/03)
A practical and efficient methodology for the laboratory scale preparation of Sch?llkopf's bis-lactim ether chiral auxiliaries (3S)- and (3R)-3,6-dihydro-2,5-diethoxy-3-isopropyl-pyrazine has been developed. The key step is the preparation of the 2,5-diketopiperazine derivative by microwave-assisted heating in water. The protocol avoids reactions at low temperature and the use of high boiling solvents. Only inexpensive and readily available starting materials are required. The bis-lactim ethers were produced in high yields on a multigram scale.
Efficient asymmetric synthesis of biologically important tryptophan analogues via a palladium-mediated heteroannulation reaction
Ma,Liu,Li,Flippen-Anderson,Yu,Cook
, p. 4525 - 4542 (2007/10/03)
A novel and concise synthesis of optically active tryptophan derivatives was developed via a palladium-catalyzed heteroannulation reaction of substituted o-iodoanilines with an internal alkyne. The required internal alkyne 14a or 25 was prepared in greater than 96% de via alkylation of the Schoellkopf chiral auxiliary 19 employing diphenyl phosphate as the leaving group. The Schoellkopf chiral auxiliary was chosen here for the preparation of L-tryptophans would be available from D-valine while the D-isomers required for natural product total synthesis would originate from the inexpensive L-valine (300-g scale). Applications of the palladium-catalyzed heteroannulation reaction were extended to the first asymmetric synthesis of L-isotryptophan 38 and L-benz[f]tryptophan 39. More importantly, the optically pure 6-methoxy-D-tryptophan 62 was prepared by this protocol on a large scale (>300 g). This should permit entry into many ring-A oxygenated indole alkaloids when coupled with the asymmetric Pictet-Spengler reaction. In addition, an improved total synthesis of tryprostatin A (9a) was accomplished in 43% overall yield employing this palladium-mediated process.
Entry into 6-methoxy-D(+)-tryptophans. Stereospecific synthesis of 1-benzenesulfonyl-6-methoxy-D(+)-tryptophan ethyl ester
Allen,Hamaker,La Loggia,Cook
, p. 2077 - 2102 (2007/10/02)
A strategy for the synthesis of optically active ring-A methoxylated indole alkaloids which employs the Moody azide/Schollkopf chiral auxiliary protocol has resulted in the successful preparation of 1-benzenesulfonyl-6-methoxy-D(+)-tryptophan ethyl ester 16. This amino ester is required for the synthesis of Alstonia bisindole alkaloids including macralstonine 2 via an enantiospecific Pictet-Spengler reaction
