Cascade Cyclization via a 4-exo-dig-Cyclocarbopalladation for an Easy Access to New Polycyclic Structures

Abstract

The 5-exo-dig-cyclocarbopalladation is a known reaction although the functionality present on the substrates used is generally limited. This reaction was performed on our original substrates propargylic diols 2a-c and 3a-c gave encouraging results. Once the analogs α-bromopropargylic diols were used, the 4-exo-dig-cyclocarbopalladation turns out to be a new possible way to prepare bicyclic compounds containing a strained 1,2-cyclobutanediol. This process is associated with a Stille cross-coupling that can be ended in some cases by a 6π-electrocyclization. This reaction sequence can thus achieve an increase in structural complexity from readily available starting materials, in a one-pot operation.

Key words

4-exo-dig-cyclocarbopalladation - cyclobutene - 5-exo-dig-cyclocarbopalladation - palladium - cascade cyclization - Stille-reaction - 6π-electrocyclization

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16

In presence of Pd(PPh₃)₄, the process was unsucessfully when carried out in polar solvents e.g. THF, DMF, NMP and CH₃CN.