Showing papers by "Matthias Breuning published in 2009"
TL;DR: The CuCl(2) complex of the tricyclic 9-oxabispidine, which carries an 2-endo,N-anellated piperidine ring, is an excellent catalyst for enantioselective Henry reactions giving the S-configured beta-nitro alcohols in 91-98 % ee (13 examples).
Abstract: A flexible approach, applica- ble on a gram scale, to chiral 2-endo- substituted 9-oxabispidines was devel- oped. The key intermediate, a cis-con- figured 6-aminomethylmorpholine-2- carbonitrile, was prepared from (R)-3- aminopropane-1,2-diol and 2-chloro- A The 2-endo substituent was introduced by Grignard addition, cyclization, and exo-selective reduction, thus furnishing the enantiomerically pure bi- and tricyclic 9-oxabispidines in 19-59 % yield. The CuCl2 complex of the tricyclic 9-oxabispidine, which car- ries an 2-endo,N-anellated piperidine ring, is an excellent catalyst for enan- tioselective Henry reactions giving the S-configured b-nitro alcohols in 91- 98 % ee (13 examples). Surprisingly, the analogous copper complexes of the bi- cyclic 9-oxabispidines delivered the enantiocomplementary R-configured products in 33-57 % ee. The respective transition states were discussed.
51 citations
TL;DR: The 9-oxabispidines synthesized were evaluated as the chiral ligands in the Pd(II)-catalyzed oxidative kinetic resolution of secondary alcohols giving good to excellent selectivity factors of up to 19.3.
Abstract: A new and flexible route to enantiomerically pure bi- and tricyclic 9-oxabispidines has been developed with use of (1R,5S)-7-methyl-2-oxo-9-oxa-3,7-diazabicyclo[3.3.1]nonane-3-carboxylic acid tert-butyl ester as the common late-stage intermediate. The 9-oxabispidines synthesized were evaluated as the chiral ligands in the Pd(II)-catalyzed oxidative kinetic resolution of secondary alcohols giving good to excellent selectivity factors of up to 19.
29 citations
TL;DR: A novel one-pot procedure for the stereoselective synthesis of alpha-hydroxy esters from ortho esters was developed and key steps were multi-heteroatom Cope rearrangements of O-acylated N-Hydroxy-l-tert-leucinol-derived oxazoline N-oxides.
18 citations
TL;DR: An enantioselective route to four tricyclic amino acids and N-tosylamides, composed of a central norbornane framework with a 2-endo,3-endo-annelated pyrrolidine ring and a 5-endo -C2 side chain, has been developed.
Abstract: An enantioselective route to four tricyclic amino acids and N-tosylamides, composed of a central norbornane framework with a 2-endo,3-endo-annelated pyrrolidine ring and a 5-endo-C1 or -C2 side chain, has been developed. A key intermediate was the chiral, N-Boc-protected ketone (1R,2S,6S,7R)-4-azatricyclo[5.2.1.02,6]decan-8-one, available from inexpensive endo-carbic anhydride in five steps and 47% yield. The rigid scaffold makes these amino acid derivatives promising candidates for β-turn-inducing building blocks in peptidomimetics and for chiral auxiliaries in asymmetric organocatalysis.
5 citations
TL;DR: In this paper, 9-oxabispidines were deprotonated at -78 °C by s-BuLi at one of the bridgehead carbon atoms to give α-lithio ethers, which were trapped with electrophiles in good yields.
Abstract: Bi- and tricyclic 9-oxabispidines are smoothly deprotonated at -78 °C by s-BuLi at one of the bridgehead carbon atoms to give α-lithio ethers, which were trapped with electrophiles in good yields. Rearrangements to ring-contracted N,O-acetals occurred upon warming in the absence of an electrophile. The α-lithio ether intermediates are presumably stabilized by negative hyperconjugation.
2 citations