By the acetoxy group

They are derivatives of 7-aminocephalosporanic acid (37) in which the RCO group is replaced by hydrogen and R by the acetoxy group. Penicillins and cephalosporins are interconvertible as indicated in Scheme 8, in which the sulfoxide-sulfenic acid rearrangement (see Chapter 4, p. 52) has been applied in the preparation of the pharmaceutically important cephalosporin (39) from the semisynthetic penicillin (32). 

In (22) participation is improbable, and certainly none can occur in the deoxy compound (23). The rate of reaction of (22) was, in fact, twice that of (21), and that of (23) was too fast to measure. For this series, at any rate, it would appear that participation by the acetoxy group on C-2 does not facilitate the reaction. It is interesting that the rate of acetolysis decreases with increasing size of the group on C-2 (23) > (22) > (21). 

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. 

In some instances, the resist polymer can be prepared in a single step by direct polymerization of the protected monomer(s) (37,88), entirely avoiding the intermediate PHOST. HOST-containing resist polymers have also been prepared by free-radical copolymerization of a latent HOST and a stable, acid-labile monomer, eg, the copolymerization of acetoxystyrene with tert-huty acrylate, followed by selective removal of the acetoxy group (89) (Fig. 30). 

Aminosodium salt and acylated with 1 H-tetrazole-1 -acetyl chloride. The acetoxy group is then displaced by reaction with 5-methyl-1,3-4-thi-adiazole-2-thiol in buffer solution. The product acid is converted to the sodium salt by NaHCOa. 

The aziridine aldehyde 56 undergoes a facile Baylis-Hillman reaction with methyl or ethyl acrylate, acrylonitrile, methyl vinyl ketone, and vinyl sulfone [60]. The adducts 57 were obtained as mixtures of syn- and anfz-diastereomers. The synthetic utility of the Baylis-Hillman adducts was also investigated. With acetic anhydride in pyridine an SN2 -type substitution of the initially formed allylic acetate by an acetoxy group takes place to give product 58. Nucleophilic reactions of this product with, e. g., morpholine, thiol/Et3N, or sodium azide in DMSO resulted in an apparent displacement of the acetoxy group. Tentatively, this result may be explained by invoking the initial formation of an ionic intermediate 59, which is then followed by the reaction with the nucleophile as shown in Scheme 43. 

The acetoxy group is introduced exclusively at the benzylic carbon. This is in accord with the intermediate being a weakly bridged species or a benzylic cation. The addition of bromide salts to the reaction mixture diminishes the amount of acetoxy compound formed by shifting the competition for the electrophile in favor of the bromide ion. Chlorination in nucleophilic solvents can also lead to solvent incorporation, as, for example, in the chlorination of 1-phenylpropene in methanol.37... 

Treatment of the iV-protected 4-chloro-2-pyridone 151 with sodium prolinate in hot DMSO gives a prolinylpyr-idone, which may then be cyclodehydrated by acetic anhydride to give the pyridopyrrolizinone 152 <1994TL6985> (Scheme 42). The acetoxy group in 152 forms the basis for further functional group transformations, as outlined in... 

Addition of l,3-bis(methylthio)allyllithium to aldehydes, ketones, and epoxides followed by mercuric ion-promoted hydrolysis furnishes hydroxyalkyl derivatives of acrolein5 that are otherwise available in lower yield by multistep procedures. For example, addition of 1,3-bis-(methylthio)allyllithium to acetone proceeds in 97% yield to give a tertiary alcohol that is hydrolyzed with mercuric chloride and calcium carbonate to saturated aldehyde.8 Similarly, addition of l,3-bis(methylthio)allyl-lithium to an epoxide, acetylation of the hydroxyl group, and hydrolysis with mercuric chloride and calcium carbonate provides a 5-acetoxy-a,/ -unsaturatcd aldehyde,6 as indicated in Table I. Cyclic cis-epoxides give aldehydes in which the acetoxy group is trans to the 3-oxopropenyl group. 

Acetylation of the hydroxy group and hydrolysis of the acetoxy group oxidation of the hydroxy group by Mn02 in ether or alternatively by Dess-Martin periodinane, and the reduction of the obtained aldehyde by NaBH4. 

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