130874-91-8Relevant articles and documents
Microwave assisted synthesis of enantiomerically pure allylboronates
Cmrecki, Vesna,Eichenauer, Nils C.,Frey, Wolfgang,Pietruszka, J?rg
experimental part, p. 6550 - 6564 (2010/10/19)
Stable allylboronates with a stereogenic centre α to the boronic ester moiety represent versatile reagents for stereoselective synthesis of homoallylic alcohols. Use of microwave irradiation in desilylation and sigmatropic rearrangement reactions allows r
Synthesis of enantiomerically pure cyclopropanes from cyclopropylboronic acids
Luithle, Joachim E.A.,Pietruszka, Joì?rg
, p. 8287 - 8297 (2007/10/03)
A general method for the stereocontrolled synthesis of cyclopropanes is described. Various, highly stable, enantiomerically pure alkenylboronic esters 13 have been conveniently synthesized by the direct hydroboration of alkynes 11 using the new chiral 1,3,2-dioxaborolane 15. The high stability was also demonstrated by the selective deprotection of a tert- butyldimethylsilyl protecting group without hydrolyzing the boronic ester. The diastereoselective cyclopropanation of the olefins was achieved by the palladium(II) acetate catalyzed decomposition of diazomethane. This process was optimized giving cyclopropylboronic esters 20/21 in high yield (89-99%) and with good to excellent diastereomeric ratios (up to 95:5). The diastereomers were separated by means of MPLC and their configurations determined by X-ray crystallography (compound 21c), by transformation to known cyclopropanols, and by correlation of NMR data. Treatment with LiAlH4 followed by acidic hydrolysis yielded the enantiomerically pure cyclopropylboronic acid 27 for the first time and allowed the nearly quantitative recovery of the chiral auxiliary 3. Different protocols for the Suzuki coupling reaction of compound 27 were investigated.