Fluorinated alcohols: A magic medium for the synthesis of heterocyclic compounds

Transition‐Metal‐Free Synthesis of N‐Hydroxy Oxindoles by an Aza‐Nazarov‐Type Reaction Involving Azaoxyallyl Cations

“…Based on these results and previous mechanistic studies of azaoxyally cations, [17][18][19][20][21] we hereby propose one possible pathway in Scheme 6. [18][19][20][21]27] To conclude,w ed eveloped at ransition-metal-free method to construct oxindoles by an aza-Nazarov-type reaction involving azaoxyallyl cation intermediates.T he reaction can be carried out under very mild reaction conditions and has broad functional-group tolerance.I n addition, ao ne-pot procedure was developed to make the method yet more practical. [28] In the azaoxyallyl cation, the lone pair of electrons on the hydroxy played ap ivotal role in stabilizing the cation.…”

HFIP‐Mediated Decarboxylative [4+3]‐Annulation of Azaoxyallyl Cations with Isatoic Anhydride

“…of HFIP to accelerate the cycloaddition of 1 a with 2 a. HFIP is a widely used solvent and additive in organic synthesis because of its unique properties, such as strong hydrogen bond donation, low nucleophilicity, and high ionizing power. [19] In particular, cycloadditions of azaoxyallyl cations have been shown to often proceed well in HFIP solution. [13][14][15] Surprisingly, α-substituted amino ester 3 not seven-membered 1,4-benzodiazepinedione, which was derived from the decarboxylative substitution of the isatoic anhydride with HFIP and the aza-substitution of α-bromohydroxamate, was obtained as the major product in this reaction (Scheme 3, eq 2).…”

“…However, replacing Na 2 CO 3 with other inorganic (K 2 CO 3 , Cs 2 CO 3 , K 3 PO 4 ) or organic (Et 3 N, DBU, DABCO, DMAP) bases did not improve the yield, although the reaction rate of the first step was higher in all the cases. Then, 4 Å molecular sieves were added to prevent the hydrolysis of the amide or ester, and the yield increased slightly ( [17][18][19][20]. A further enhancement in the yield of 4 aa was observed upon increasing the reaction temperature, and the highest yield (79%) was achieved when second step was carried out under reflux ( Table 1, entry 21).…”

Selection of microbial biocatalysts for the reduction of cyclic and heterocyclic ketones

“…Consequently, great effort has been made for designing efficient strategies to prepare substituted heterocyclic compounds [8]. Among them, the reduction of carbonyl compounds plays an important role because the reduction of prochiral ketones to chiral alcohols is an excellent way to generate chirality in the synthesis of a molecule.…”