A new method for the generation of benzyl radicalsfrom acetals via low-valent titanium-mediated homolytic C–O bond cleavage is presented. The low cost and availability of the developed titanium reagent enable efficient access to α-alkoxy carbon radicalspecies via the developed reaction.
Hexabromoacetone (HBA) was efficiently used for the protection of alcohols and aldehydes and deprotection of benzaldehyde dimethyl acetal, solketal, and other acetals and ketals. In only 10 min, the protection of glycerol yielded 90% of solketal and protection of benzaldehyde gave 95% of benzaldehyde dimethyl acetal. The deprotection of benzaldehyde dimethyl acetal under UV irradiation gave over 90%
Shell Cross‐Linked Micelles as Nanoreactors for Enantioselective Three‐Step Tandem Catalysis
作者:Michael Kuepfert、Aaron E. Cohen、Olivia Cullen、Marcus Weck
DOI:10.1002/chem.201804956
日期:2018.12.12
enantio‐enriched alcohols in the cross‐linked shell, and nucleophilic base‐catalyzed acylation in the hydrophobic core. The catalysts are positioned in close proximity on a single micelle support to take advantage of the intramicellar substrate diffusion, yet they are sufficiently spaced apart from each other in physically distinct microenvironments. These compartmentalized micelles are substrate selective
A highly efficient metal-free aldol-type reaction of various acetals or ketals with fluorinated silylenolethers catalysed by less than 1 mol% HClO4 (70 wt%, aq.) is developed. This provides expedient access to a wide array of valuable fluoroalkyl ethers featuring a ketone carbonyl functionality in good to excellent yields (40 examples). Furthermore, the thus obtained adducts are readily elaborated
Halogenative Deoxygenation of Ketones; Vinyl Bromides and/or<i>gem</i>-Dibromides by Cleavage of 1,3-Benzodioxoles (Ketone Phenylene Acetals) with Boron Tribromide
Representative ketones 1 have been converted in generally good yields to the respective 1,3-benzodioxoles 5 by trans-acetalization of ketone dimethyl acetals with 1,2-dihydroxybenzene, and cleaved with boron tribromide. 1, 3-Benzodioxole derived from α-unbranched aliphatic ketones gave in general a mixture of vinyl bromides and gem-dibromides; pure gem-dibromides could be selectively obtained in most of cases using a suitable reaction time. 1, 3-Benzodioxoles derived from α-branched ketones gave complex mixtures and their cleavage appears to be of little synthetic significance. 1,3-Benzodioxoles of aromatic ketones gave vinyl bromides only. Aliphatic cyclic gem-dibromides 3 were converted to the respective vinyl bromides 2 by phase-transfer-catalysed dehydrobromination.