4-Chlorobutyryl group was used as amino protective group for n(-)-alpha-phenylglycine (I). N-Hydroxysuccinimide ester III was prepared in high yield but partly racemic. Reaction of III or IV with V afforded epimeric mixtures of N,0-protected cephalexins (VI), which can be separated by crystallisation. The 4-chlorobutyryl group in VII was removed under very mild conditions giving cephalexin (IX)...

The stereoselective addition of the titanium (IV) enolates derived from (S)-4-isopropyl-N-4-chlorobutyryl-1,3-thiazolidine-2-thione (8) and from (S)-4-isopropyl-N-4-chloropentanoyl-1,3-thiazolidine-2-thione (9) to N-Boc-2-methoxypyrrolidine (5b) afforded the addition products (+)-10 and (+)-11 in 84% yield in both cases, as 8.6:1 and 10:1 diastereoisomeric mixtures, respectively. A threestep se...