page_title: Büchner–Curtius–Schlotterbeck reaction
section_title: Reaction Mechanism
hierarchical_section_title: Büchner–Curtius–Schlotterbeck reaction / Reaction Mechanism
caption_attribution_description: English: The production of the two carbonyl products from the carbocation intermediate
context_page_description: The Buchner–Curtius–Schlotterbeck reaction is the reaction of aldehydes or ketones with aliphatic diazoalkanes to form homologated ketones. It was first described by Eduard Buchner and Theodor Curtius in 1885 and later by Fritz Schlotterbeck in 1907. Two German chemists also preceded Schlotterbeck in discovery of the reaction, Hans von Pechmann in 1895 and Viktor Meyer in 1905. The reaction has since been extended to the synthesis of β-keto esters from the condensation between aldehydes and diazo esters. The general reaction scheme is as follows:
  The reaction yields two possible carbonyl compounds along with an epoxide (III). The ratio of the products is determined by the reactant used and the reaction conditions.
context_section_description: The general mechanism is shown below. The resonating arrow (1) shows a resonance contributor of the diazo compound with a lone pair of electrons on the carbon adjacent to the nitrogen. The diazo compound then does a nucleophilic attack on the carbonyl-containing compound (nucleophilic addition), producing a tetrahedral intermediate (2). This intermediate decomposes by the evolution of nitrogen gas forming the tertiary carbocation intermediate (3).
  The reaction is then completed either by the reformation of the carbonyl through an 1,2-rearrangement or by the formation of the epoxide. There are two possible carbonyl products: one formed by migration of R₁ (4) and the other by migration of R₂ (5).  The relative yield of each possible carbonyl is determined by the migratory preferences of the R-groups.
  The epoxide product is formed by an intramolecular addition reaction in which a lone pair from the oxygen attacks the carbocation (6).
  This reaction is exothermic due to the stability of nitrogen gas and the carbonyl containing compounds.  This specific mechanism is supported by several observations.  First, kinetic studies of reactions between diazomethane and various ketones have shown that the overall reaction follows second order kinetics.   Additionally, the reactivity of two series of ketones are in the orders Cl₃CCOCH₃ > CH₃COCH₃ > C₆H₅COCH₃ and cyclohexanone > cyclopentanone > cycloheptanone > cyclooctanone.  These orders of reactivity are the same as those observed for reactions that are well established as proceeding through nucleophilic attack on a carbonyl group.
caption: Mechanisms for formations of the carbonyl products
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