Trisubstituted cyclooctene synthesis at the limits of relay ring-closing metathesis: a racemic difluorinated analogue of fucose
摘要:
A telescoped sequence based on metallated enol acetal chemistry allowed the efficient delivery of a ring-closing metathesis (RCM) precursor, which was used to form a cyclooctenone product with a trisubstituted alkenyl group in moderate yield, though a high loading of second generation Grubbs pie-catalyst was required. A relay RCM (RRCM) precursor was synthesised to deliver the key alkylidene at a higher rate; the catalyst loading required was high. and increasing the reaction temperature simply resulted in the loss of the cyclising alkylidene by a non-productive cross-metethesis pathway We were forced to use high dilution conditions to suppress the unwanted CM and secure the cyclooctenone product The cyclooctenone product could be progressed to analogues of fucose and 6-deoxyidose by UpJohn dillydroxylation. (C) 2009 Elsevier Ltd. All rights reseived
Cornforth–Evans Transition States in Stereocontrolled Allylborations of Epoxy Aldehydes
作者:Robert R. A. Freund、Matthias Borg、Daniel Gaissmaier、Robin Schlosser、Timo Jacob、Hans‐Dieter Arndt
DOI:10.1002/chem.202001479
日期:2020.7.14
(CE) model for alkoxy‐ and epoxy‐substitutedaldehydes. CE‐type transition states were uniformly identified as minima in advanced, DFT‐based computational studies of allylboration reactions of epoxy aldehydes, conforming well to the experimental data, and highlighting the underestimated relevance of this model. Furthermore, a mechanism‐based rationale for the substitution pattern of the epoxide was delineated