Synthesis of new carbohydrate-derived ketones as organocatalysts in the enantioselective epoxidation of arylalkenes. Part 2: Chiral ketones from sugars

New mannose-derived ketones as organocatalysts for enantioselective dioxirane-mediated epoxidation of arylalkenes. Part 3: Chiral ketones from sugars

“…Our preliminary essays chose trans-stilbene as a testing model olefin, and ketone 18 as catalyst, indicating similar reactivity to our previously described ketones. 17,18 When we employed sub-stoichiometric quantities (0.5 equiv) of ketone, the reaction time was high (1e2 days) and conversion was low under these conditions (recovering alkene without epoxidation). Increasing the amount of ketone allowed us to improve the efficiency of the epoxidaton reaction (yields and reaction times) but without changing stereochemical results (ee and major oxirane configuration).…”

“…We have employed them in dioxirane-mediated epoxidation of arylalkenes obtaining moderate-to-good excesses. Best ee's were obtained with compound 9, a-methyl-D-galacto derivative 18 (Fig. 4).…”

Synthesis and Applications of Carbohydrate-Based Organocatalysts

“…Based on both the reports of Shing [ 116 , 123 , 124 ] and Shi [ 11 , 113 ] regarding the dioxirane-mediated stereoselective epoxidation using carbohydrate-derived catalysts and their own experience in the application of sugar derivatives in asymmetric reactions [ 125 , 126 , 127 ], Vega-Pérez, Iglesias-Guerra and their co-workers synthesised new sugar-based ketones [ 128 , 129 , 130 ]. In addition to various unsymmetrical ketones bearing a single carbohydrate unit, one C 2 -symmetric sugar ketone was also prepared.…”

“…The α and β d -glucopyranose and d -galactopyranose ketones 252a-c and 255a-c ( Scheme 68 ) were also synthesised applying the same reaction sequence described for the synthesis of 249 [ 128 , 129 ]. Moreover, aiming to check the influence of the anomeric stereocenter in glucose-derived catalysts 252a-c , the authors prepared the 1-deoxygenated analogue 258 starting from the 4,6- O -benzylidene derivative 256 ( Scheme 68 ).…”

“…Furthermore, the character of a substituent in anomeric position (aromatic vs. aliphatic) had no influence on the enantioselectivity in case of glucose-derived catalysts, whereas for galactose-derived analogues it was observed that aromatic groups led to lower enantiomeric excess [ 128 , 129 ]. Finally, the epoxidation of the more challenging cis -olefins h-j ( Scheme 69 ) did not take place using either glucose- ( 252b,c ) or galactose-derived ( 255a ) catalysts [ 129 ].…”