[11C]Phosgene: A Versatile Reagent for Radioactive Carbonyl Insertion Into Medicinal Radiotracers for Positron Emission Tomography

[11C]Phosgene has been playing a relatively modest but continuous and manifest role all along the history of radiochemistry for Positron Emission Tomography. It acts as a radiolabelling agent through carbonyl insertion, usually between heteroatoms, and benefits from a high chemical reactivity allowing for short reaction times. The aim of this review is to give an overview of this radiochemistry from its beginning until the present day. After drawing up the inventory of the various ways of its production, the reactions in which it has been employed and the labelled products that have been synthesised with it are catalogued. This comprises the reactions of [11C]phosgene with primary, secondary and tertiary amines to labelled isocyanates and carbamoyl chlorides, which serve as intermediates for symmetrical and unsymmetrical [11C]ureas and [11C]carbamates, reactions with alcohols leading to labelled carbamates and carbonates via [11C]chloroformates, cyclisation reactions to heterocycles and the radiochemistry of the secondary radiolabelling agents [11C]urea and diethyl- or dimethyl [11C]carbonate. Apart from this already vast field of chemical possibilities there should be room for extension of the use of [11C]phosgene to other chemistry, notably that of C-11C bond formation.