Optimization of Bingel's synthesis in the presence of amino acids and dimethyl sulfoxide without a base.

Entry	Catalyst	C6H5Cl : DMSO (v/v)	Yield of 1, %
1	—	2 : 1	0
2	N-Ethylglycine	2 : 1	37
3	Glycine	2 : 1	33
4	N-Benzylglycine	2 : 1	38
5	Sarcosine	2 : 1	42
6	Sarcosine	20 : 1	5
7	Sarcosine	20 : 3	8
8	Sarcosine	4 : 1	17
9	Sarcosine	5 : 2	39
10	Sarcosine	5 : 3	41
11	Sarcosine	4 : 3	38