Bis(oxazolines) based on glycopyranosides – steric, configurational and conformational influences on stereoselectivity

• Tobias Minuth and
• Mike M. K. Boysen

Beilstein J. Org. Chem. 2010, 6, No. 23, doi:10.3762/bjoc.6.23

• depended on the steric demand of the 3-O-substituents. To further probe the impact of the 3-position of the pyranose scaffold, we prepared 3-epimerised and 3-defunctionalised versions of these ligands as well as a 3-O-formyl derivative. Application of these new ligands in asymmetric cyclopropanation

• revealed strong steric and configurational effects of position 3 on asymmetric induction, further dramatic effects of the pyranose conformation were also observed. Keywords: asymmetric synthesis; carbohydrates; copper; cyclopropanation; ligand design; Introduction The design and optimisation of chiral

• ligands were subsequently employed in the asymmetric cyclopropanation [22][23] of styrene (4) with ethyl diazoacetate (5). Our results revealed a strong dependence of the enantioselectivity on both the steric bulk and electronic nature of the O-substituents in ligands 2a–c and 3a–f. Furthermore, the

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• the requisite 5-halopyrrolidinone precursor. 5.5. Cha. Dialkoxytitanacyclopropane addition to imides This methodology provides a very elegant way to install the C9a hydroxyl group, which remains the biggest challenge of mitomycin synthesis. Based on the precedent of ester cyclopropanation in presence

• of a titanocyclopropane developed by Kulinkovich [116], Cha’s approach to mitomycins involves the intramolecular addition of the same dialkoxytitanacyclopropane to an imide [117]. In contrast to the Kulinkovich’s cyclopropane synthesis, the imide proved to be resistant to cyclopropanation and the

Asymmetric reactions in continuous flow

• Xiao Yin Mak,
• Paola Laurino and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2009, 5, No. 19, doi:10.3762/bjoc.5.19

• using a silica-supported chiral Co(salen) complex [42]. Asymmetric cyclopropanation has also been studied in continuous flow, using monolithic reactors immobilized with chiral PyBox ligands [43][44]. The cyclopropanation of stryrene with ethyldiazoacetate was investigated as a model reaction for this

• ). Continuous-flow asymmetric cyclopropanation. Continuous asymmetric hydrogenation of dimethyl itaconate in scCO2. Continuous asymmetric transfer hydrogenation of acetophenone. Asymmetric epoxidation using a continuous flow membrane reactor. Enzymatic cyanohydrin formation in a microreactor. Resolution of (R/S

Allylsilanes in the synthesis of three to seven membered rings: the silylcuprate strategy

• Asunción Barbero,
• Francisco J. Pulido and
• M. Carmen Sañudo

Beilstein J. Org. Chem. 2007, 3, No. 16, doi:10.1186/1860-5397-3-16

• -step pathway involving firstly, Me3Al-catalysed intramolecular cyclization of the oxoallylsilane and subsequent formation of a methylenecyclopentanolate, and then cyclopropanation. This unique mechanism enables the construction of hydroxylated bi-tri- and tetracyclic skeletons, bearing the spiro

• . Intramolecular cyclization of TMS-epoxyallylsilanes. Spiro-cyclopropanation from oxoallylsilanes. Cyclobutane formation from hydroxy-functionalized allysilanes. Cyclobutene formation from vinyltin cuprates and epoxides. Silylcupration of 1,2-propadiene and reaction with α,β-unsaturated nitriles. Cycloheptane