Leaving groups for nucleophilic

Phosphate esters have a variety of mechanistic paths for hydrolysis. Both C-O and P-0 cleavage are possible depending on the situation. A phosphate monoanion is a reasonable leaving group for nucleophilic substitution at carbon and so 8 2 or SnI reactions of neutral phosphate esters are well known. PO cleavage can occur by associative (by way of a pentacoordinate intermediate), dissociative (by way of a metaphosphate species), or concerted (avoiding both of these intermediates) mechanisms. 

Nitration of furfuryl alcohol (2-furylmethanol) in acetic anhydride yields the nitro-nitrate 57 which possesses both a reactive methylene group able to undergo aldol reactions, etc., and also a nitrate ion leaving group for nucleophilic substitutions.137 Detailed studies of the nitration disclose various products resulting from the addition of one or even two acetic acid residues to the furan nucleus in competition with the nitrations.138,139... 

T. Netscher, Sulfonate leaving groups for nucleophilic substitution reactions-improved structures and procedures. Recent Research Developments in Organic Chemistry, 2003, 7,71-83. 

Fig. 1. Nucleophilic substitutions as strategy for the use of unprotected, pharmacophore-rich reagents. FG, functional group Nu, nucleophile PG, protective group Pol, polymeric support X, leaving group for nucleophilic displacement.

Heterocycles Containing More Than Two Heteroatoms 573 Benzotriazolyl is a useful leaving group for nucleophilic substitutions in 1,2,3-thiadiazoles. ... 

Table 7.2 Good Leaving Groups for Nucleophilic Substitution...

---