Common Reaction Types in Heterocyclic Chemistry 15Another advantage of the Minisci reaction is that very simple conditions are used – aqueous sulfuric acid, with an oxi-
dant and sometimes a catalyst [Fe(II) or Ag(I)]. These oxidising conditions generate the radicals and also re-aromatise
the initial product of radical addition. Additionally, protonation of the imine nitrogen greatly increases the susceptibility
of the heterocycle to nucleophilic radical addition, which takes place at the imine carbon.
The four examples illustrate the use of the Minisci process for pyridine, a quinoline, a pyrimidine and a benzothiazole,
where the imine unit is in a fi ve-membered ring.
C-Metallated heterocycles as nucleophiles
Organometallics, especially organolithium intermediates, are very frequently used in heterocyclic chemistry. The gen-
eration and use of organolithium intermediates must generally be conducted at very low temperatures, typically that
of an acetone–dry ice (solid CO 2 ) cooling bath (78 °C). Organolithiums are nucleophiles, thus reaction with ketones
and aldehydes gives alcohols following ‘aqueous work-up’. In the remaining chapters, chemical schemes which include
reactions of lithium derivatives do not explicitly show the intermediate, or the addition of water, but the requirement
for an ‘aqueous work-up’ must always be kept in mind.
Also very useful are the reactions of organolithium nucleophiles with N,N-dimethylformamide (DMF), with disulfi des
(RS-SR), with halogen donors such as BrCCl 2 CCl 2 Br, with trialkyl borates (e.g. B(OMe) 3 ), and with chlorotrialkylstan-
nanes (e.g. n-Bu 3 SnCl). In the fi rst case, an aldehyde is the product, in the second case a sulfi de, in the third case a halide
is the product and in the last two, heteroarylstannanes and heteroarylboronic acids result.