(S)-1,1'-Binaphth-2-ol (BINOL) in combination with ZnEt(2), Ti(O(i)Pr)(4), and biscyclohexylamine was found to catalyze the highly enantioselective (83-95% ee) addition of various 1,3-diynes to aldehydes of diverse structures. This method provides a convenient pathway to generate a number of optically active dienediynes as the acyclic precursors to polycyclic compounds. The chiral dienediynes undergo highly chemoselective Pauson-Khand (PK) cycloaddition in benzaldehyde by using [Rh(cod)Cl](2) as the catalyst in the presence of rac-BINAP. High diastereoselectivity (up to >20:1) has also been achieved with the chiral dienediyne substrates containing a bulky substituent adjacent to the chiral center. In the presence of the Grubbs II catalyst, ring-closing enyne metathesis of the PK cycloaddition products led to the formation of the desired 5,5,7- and 5,5,8-fused tricyclic compounds. Further highly diastereoselective Diels-Alder reaction of a 5,5,7-tricyclic compound with maleic anhydride produced a 5,5,7,6-polycyclic product. The asymmetric synthesis of polycyclic compounds from optically active dienediynes has established a novel and efficient synthetic route to the structural framework of many biologically significant molecules.
The s4U button has more power to catch RNA toys: There is growing interest in RNA techniques. Engineered ascorbate peroxidase (APEX2) was discovered to react with guanine, and generate RNA proximity labeling tools. But the RNA labeling efficiency still has room for improvement. We found that the metabolic incorporation of 4‐thiouridine can introduce additional reactive sites for RNA labeling, and improve the efficiency of the peroxidase‐generated biotinylation of RNA. More information can be found in the full paper by X. Weng et al.
From Highly Enantioselective Catalytic Reaction of 1,3-Diynes with Aldehydes to Facile Asymmetric Synthesis of Polycyclic Compounds. -Highly enantioselective addition of various 1,3-diynes towards aromatic and aliphatic aldehydes is smoothly achieved in the system Et2Zn-(S)-BINOL-Ti(O-iPr)4. Chiral hydroxydiynes, e.g. (III), (XIII), (XV) or (XVII), are obtained in up to 95% optical purity. O-Allylation and subsequent Pauson-Khand cyclization then provides fused tetrahydrofurans (VII)/(VIII). In the presence of a tethered alkene, metathesis reaction can be used to close a central medium-sized ring to afford tricyclic compounds, e.g. (IX), structural motifs of a variety of natural and bioactive products. -(TURLINGTON, M.; DU, Y.; OSTRUM, S. G.; SANTOSH, V.; WREN, K.; LIN, T.; SABAT, M.; PU*, L.; J. Am. Chem. Soc. 133 (2011) 30, 11780-11794, http://dx.doi.org/10.1021/ja204289q ; Dep. Chem., Univ. Va., Charlottesville, VA 22904, USA; Eng.) -Mischke 52-051
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