One-Step Conversion of Acetophenones to α-Haloacetophenone Dimethyl Acetals Using DCDMH/DBDMH and Molecular Sieve in Methanol

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

Keywords:

• Acetophenone
• 1,3-dibromo-5,5-dimethylhydantoin
• 1,3-dichloro-5,5-dimethylhydantoin
• α-haloacetophenone dimethyl acetals
• molecular sieve
• one-step conversion
• piperidine

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.