Small electrophiles

The 02 adduct has a rich chemistry of its own (Figure 3.15) reacting with small electrophiles in processes involving oxidation of the substrate. Thus NO couples to give nitrite and N204 nitrate S02 is turned into sulphate and C02 into carbonate. In several cases, as with aldehydes and ketones, a peroxychelate ring results. 

Nin-amido complexes such as (117) react with small electrophiles by insertion either in the Ni—N bond (e.g., with C02 to form (118)) or in the N—11 bond. With unsubstituted aryl groups (Ar = Ar = Ph), both a monomeric complex (117) or a dimeric species (119) is formed, depending on the amount of PMe3 added. Using bulky borylamide ligands, an almost linear, two-coordinate Nin complex could be obtained and structurally characterized.467 The N—Ni—N angle in (120) is 167.9°. 

When the dimetallic species 210 was first deuteriated with MeOD and then subjected to iodinolysis, a 60/40 mixture of the two diastereomeric a-deuteriated iodides 267a and 267b was obtained. Although the use of a first small electrophile such as a MeOD did not enable efficient differentiation of the two carbon-metal bonds, a reversal of diastereose-lectivity was observed when the a-deuteriated dimetallic species 268 was first protonated with MeOH and then reacted with iodine. This result points towards the configurational stability of the resulting monoorganozinc species generated after reaction with a first electrophile, presumably due to the coordination by fert-butyl ether moiety (equation 127)162. 

Singlet molecular oxygen (lC>2) is a very small electrophilic reagent that can produced by photosensitization and react easily with dienes and alkenes in [4 + or [2 + 2] cycloadditions or ene-reactions. In order to develop synthetic applic tions of photooxygenations, numerous studies have recently been developed wi chiral substrates and especially in the presence of chiral auxiliaries. 

Many studies have been performed on fluorinated anthraqrclines and their comparison with non-fluorinated analogues allow a better and deeper knowledge of the biological mechanisms involved in the activity of this class of drugs. We now know the influence of this small electrophilic atom, when introduced on different positions of the aglycone and sugar moiety. 

Our studies of the alkylation reaction clearly indicated that bicyclic malonates like 23 have an inherent bias to undergo alkylation on the undesired endo face and that it will be difficult to overcome this bias with small electrophiles. Because of this bias, we carried out several exploratory reactions aimed at... 

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