Mechanistic studies of an L-proline-catalyzed pyridazine formation involving a Diels–Alder reaction with inverse electron demand

• Anne Schnell,
• J. Alexander Willms,
• S. Nozinovic and
• Marianne Engeser

Beilstein J. Org. Chem. 2019, 15, 30–43, doi:10.3762/bjoc.15.3

• intermediates mimic single steps of the proposed catalytic cycle in the gas phase. Thus, the charge-tagged catalyst proved one more time its superior effectiveness for the detection and study of reactive intermediates at low concentrations. Keywords: charge-tag; electrospray ionization; enamine organocatalysis

• introduced into the analyte molecules, usually in the form of alkylated amines or phosphines [5][6]. The charge-tag can be located either within the substrate [23][24][25] or the catalyst [18][26][27]. As a result, all species containing the charge-tag will have a similarly high ESI response [6][25] while

• species that are not involved in the reaction and do not carry the charge-tag will have a much lower ESI response. A charge-tag thus facilitates “fishing” [5][23][28] for reactive intermediates. We have previously used the charge-tagged L-proline derived catalyst 1∙Cl (Figure 1) in an ESIMS study of a L

A new charge-tagged proline-based organocatalyst for mechanistic studies using electrospray mass spectrometry

• J. Alexander Willms,
• Rita Beel,
• Martin L. Schmidt,
• Christian Mundt and
• Marianne Engeser

Beilstein J. Org. Chem. 2014, 10, 2027–2037, doi:10.3762/bjoc.10.211

• position of the charge tag far away from the catalytic center in order to avoid unwanted interactions. The use of a charged catalyst leads to significantly enhanced ESI signal abundances for every catalyst-derived species which are the ones of highest interest present in a reacting solution. The new

• temporal evolution has been followed using a microreactor continuous-flow technique. Keywords: charge tag; electrospray; mass spectrometry; organocatalysis; proline; template; Introduction Electrospray ionization (ESI) mass spectrometry [1] has not only developed into a standard characterization method

• deprotection [59]. Mechanism of the Jørgensen inversed aldol reaction According to the mechanistic model for enamine catalysis from List and Houk [36][37][38], the aldol reaction from Jørgensen should proceed via the catalytic cycle shown in Scheme 4. We began our experiments with a test whether the charge tag