Ti-Dieckmann condensation

Later, Tanabe and co-workers reported a dehydration version of the Ti-Dieckmann condensation. The reaction can be considered as a... 

Tanabe et al. proposed mechanism for the dehydration-type Ti-Dieckmann condensation and thiophene formation is shown below. 

Regioselective techniques were developed to direct the cyclization of unsymmetrical esters. An interesting example of this aspect of the Dieckmann condensation is the synthesis of ip-methylcarbapenems by Tanabe and co-workers, ip-methylcarbapenems is a structure that exists in potent and broad antibacterial compounds, such as meropenem and biapenem, which renders it synthetically interesting for the synthesis of some close analogues 30a-d. Thioesters 29 was subjected to cyclization under dehydration type Ti-Dieckmann condensation conditions 3.0 equivalents of the TiCU and 3.3 equivalents of the base BusN were used to give the vinyl... 

Dieckmann condensation under basic conditions yields 3-piperidones (Equation 81) <2004JME5620>. Substituted 4-piperidones are also reported in a Ti(iv)-mediated Dieckmann condensation of diesters (Equation 82) <1995SC177>. The electroreduction of the alkenyl bromide 36 under [Ni(cyclam)](ClC>4)2-catalyzed conditions leads to the piperidone in moderate yields (Equation 83) <1996JOC677>. 

The Ti- and Zr- Claisen and Dieckmann condensations exhibit powerful reactivity to realize C-C bond formations between various carboxylic esters under mild reaction conditions. This characteristic merit would promise a large ring closing with higher concentrations and speed. 

---