6- Chloropenicillanic acid

One interesting example of S -6 participation occurs on treatment of 6-chloropenicillanic acid (117) with sodium methoxide. The pathway through esters (118) and (119) was proposed as a route to the formation of (120). Spectrophotometric evidence was gained to support the intermediacy of (119). 

An interesting rearrangement product has been obtained from nitrosation of 6-APA,and a related substance from treatment of 6-chloropenicillanic acid with nucleophiles. ... 

When 6/3-aminopenicillanic acid (6-APA) is diazotized in the presence of chloride ion, the principal product obtained is 6a-chloropenicillanic acid (38) (62JOC2668), presumably by way of the diazo intermediate (39 Scheme 29) (72JCS(P1)895). If the diazotization is carried out in the presence of excess bromide instead of chloride, significant amounts of the 6,6-dibromo derivative are obtained, and in the case of excess iodide the 6,6-diiodopenicillanic acid becomes the predominant product (69JCS(C)2123). The 6,6-dihalo products presumably arise from nitrous acid oxidation of halide to halogen, which then reacts with (39). 

Penicillanic Acid Sulfone X = Cl, 6 P-Chloropenicillanic Acid penicillanic acid... 

By contrast, 6-a-chloropenicillanic acid undergoes D-exchange at C(6) in NaOD/DjO without epimerisation and at a rate faster than p-lactam ring-opening. 6-P-Epimers appear to undergo epimerisation and deuteria-tion at C(6) at the same rate in water (Clayton et al 1969 Gensmantel et al., 1981). 

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