Abstract
Using DCDMH/DBDMH as N-halo reagent, piperidine as catalyst, and 4-A molecular sieve as water-removing agent, α-haloacetophenone dimethyl acetals were directly obtained from the solvent of methanol. As to the substrates with electron-withdrawing groups, the conversions were 80–100%.
GRAPHICAL ABSTRACT
ACKNOWLEDGMENT
The authors thank Shanghai Foundation of Science and Technology for finacial support (No. 073919106).
Notes
a 1a (10 mmol), DCDMH (20 mmol), silica gel (1 g), MeOH 35 mL, reflux for 12 h.
b The conversion to 2a was determined by 1H NMR analysis of the crude reaction mixture.
a Substrate (10 mmol), DCDMH (20 mmol), 4-A molecular sieves (15 g), piperidine (2.5 mmol), MeOH (35 mL), reflux for 12 h.
b DBDMH (20 mmol) and the reaction mixture was heated to 50–52°C for 12 h.
c The conversion to α-haloacetophenone dimethyl acetals was determined by 1H NMR analysis of the crude reaction mixture. The isolated yields were in the brackets.
d 2j, α-chloro-p-methyl-acetophenone and α,α-dichloro-p-methylacetophenone were found in the products and the ratio of the three compounds determined by 1H NMR was 2:1:1.
e 7% of the α,α-dichloroacetophenone was also found in the products determined by 1H NMR.