Piperazine → 1-Benzoylpiperazine

Mono-benzoylation of unsymmetric substituted piperazines (A and B in Scheme 33 represent, for example R14, R16, R18 and R20 once incorporated into a compound of Formula I) could be achieved by using one of the following procedures (Scheme 33), in which all the methods were exemplified by mono-alkyl substituted piperazines. (a) Unsymmetric piperazines were treated with 2 equivalents of n-butyllithium, followed by the addition of benzoyl chloride at room temperature to afford a mixture of two regioisomers, which could be separated by chromatography (Wang et al, Ref.32 and 33(b), Scheme 34 eq. 06); (b) Benzoic acid was converted to its pentafluorophenyl ester, and then further reaction with 2-alkylpiperazine to provide the mono-benzoylpiperazines with the benzoyl group at the less hindered nitrogen (Adamczyk et al, Ref. 33(a), Scheme 34, eq. 07); (c) A mixture of piperazine and methyl benzoate was treated with dialkylaluminum chloride in methylene chloride for 24 days to yield the mono-benzoylpiperazine with the benzoyl group at the less hindered nitrogen (Scheme 34 eq. 08); (d) Unsymmetric piperazines were treated with 2 equivalents of n-butyllithium, followed by subsequent addition of triethylsilyl chloride and benzoyl chloride in THF at room temperature to afford mono-benzoylpiperazines with the benzoyl group at the more hindered nitrogen (Wang et al, Ref. 33(b), Scheme 34, eq. 09). When the substituent at position 2 was a ester or amide, the mono-benzoylation with benzoyl chloride occurred at the less hindered nitrogen of the piperazine with triethylamine as base in THF (Scheme 34, eq. 10).

ORD record

ord-1bf537a5470b4d618a991445186b5825

Source dataset

uspto-grants-2003_06

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US06573262B2