Since the demonstration by Stork and Ficini in 1961 that unsaturated diazoketones undergo intramolecular cyclization to form cyclopropanes the intramolecular reactions of α-diazocarbonyl compounds have been extensively studied under thermal, catalytic, and photochemical conditions. Intramolecular cyclization of α-carbonyl carbenes and carbenoids has found widespread application to the synthesis of theoretically interesting compounds such as bullvalene, twistane, bridged annulenes, and barbaralone, as well as syntheses of natural products such as sabinene, sirenin, α-chamigrene, and phyllocladene. The reaction has also allowed the construction of several intriguing polycyclic systems that were unattainable by alternative methods.
A recent review has covered the reactions of diazoacetic esters with alkenes, alkynes, heterocyclics, and aromatic compounds. Unsaturated alkoxycarbonyl carbenes (:CHCO2R) and unsaturated carbonyl carbenes (:CHCOR) (where R contains either aromatic or olefinic groups), which are considered to be intermediates in the absence of catalyst, have been the subject of several other reviews. A review concerning photochemically, thermally, and catalytically induced Wolff rearrangements of α-diazocarbonyl compounds has recently appeared. However to date no comprehensive review has appeared which demonstrates the synthetic potential of α-diazocarbonyl insertion and addition reactions.
In reviewing the reactions of α-diazocarbonyl compounds chosen not to include certain peripheral topics such as intermolecular reactions, intramolecular dimerization of bis(α-carbonyl carbenoids) to give diacyl cycloolefins and intramolecular trimerizations of tris(α-keto carbenoids), affording triacylcyclopropanes are not included. Also excluded are base-catalyzed reactions of α-diazocarbonyl compounds and certain ring-contraction reactions involving C–C bond insertion of intermediate α-ketocarbenes.
The topics included in this report are the intramolecular reactions of α-carbonyl carbenes and carbenoids with olefinic and aromatic unsaturation, with C–H bonds, and with C–C and N–H single bonds. Also included are acid-catalyzed cyclization reactions of α-diazoketones.