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Titanium(IV)-Mediated Tandem Deprotection−Cyclodehydration of Protected Cysteine N -Amides: Biomimetic Syntheses of Thiazoline- and Thiazole-Containing Heterocycles

2000; American Chemical Society; Volume: 2; Issue: 21 Linguagem: Inglês

10.1021/ol000178q

1523-7060

Prakash Raman, Hossein Razavi, Jeffery W. Kelly,

Sulfur-Based Synthesis Techniques

The scope and limitations of TiCl(4)-mediated Delta(2)-thiazoline synthesis via tandem deprotection-dehydrocyclization of trityl-protected cysteine N-amides is presented. While chemical yields are acceptable (53-96%), the stereochemical outcomes vary on the basis of structural considerations and reaction conditions (22-99% ee). Racemization at the C(2)-exomethine position limits the utility of this method for the formation of a thiazoline within a peptide. Treatment of a tritylated Cys-Cys dipeptide with TiCl(4) afforded the corresponding thiazole-thiazoline heterocycle 12 (38% yield, 97% ee).