Diastereoselective reactions 3- thiazolidine-2-thione

A new reaction of iV-acyl thiazolidinethione enolates with enolizable aldoxime ethers has been reported to give 2-(thiazolidine-2-thione)-l-azetines 608 with excellent diastereoselectivity (Equation 235) <2003JA3690>. The absence of either a methoxy or a carbonyl group in the 1-azetines indicated a complex mechanism rather than a simple addition reaction. The formation of azetines has been rationalized by combination of the oxime and TiCh to give a highly electrophilic trichlorotitanium iminium intermediate 609, which adds onto enolate 610 to form intermediate 611, which cyclizes to azetidines 612 (Scheme 81). An irreversible elimination of bis-trichlorotitanium oxide provides the ultimate driving force to produce azetines. 

A new efficient methodology for the preparation of a chiral 2-azetidinone intermediate applicable to the total synthesis of (+)-thienamycin and l)S-substituted carbapenems has been developed (86JAa673). This is based on the highly diastereoselective aldol-type reaction employing C4-chiral 3-acyl-l,3-thiazolidine-2-thiones and 4-acetoxy-2-azetidinones. 

Diastereoselective Aldol Reactions. The tin(II) enolate generated from 3-propionylthiazolidine-2-thione (1), tin(II) trifluoromethanesulfonate, and 1-ethylpiperidine reacts with aldehydes at —78 °C to afford the aldol adducts in high yields with high syn selectivities (eq 1). 3-Acetylthiazolidine-2-thione (2) (bp 125-128 °C/2 mmHg) and 3-(3-phenyl-propanoyl)thiazolidine-2-thione (3) (mp 66.0-67.5 °C) also work well under the same reaction conditions. 

Figure 11.51 Diastereoselective aldol reactions with (S)-3-f C2]acetyl-4-isopropyl-1,3-thiazolidine-2-thione...

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