Science of Synthesis

Wang, S.-H.; Tu, Y.-Q.; Tang, M., Science of Synthesis: Applications of Domino Transformations in Organic Synthesis, (2015) 1, 306.

The second type of functional group that can be used as the initiator for ring-closure procedures are carbonyls and their derivatives, such as O,O- and O,N-acetals (‌Scheme 38‌). Due to the presence of the electronegative oxygen or nitrogen atom, such functional groups can interact with Lewis acids to give a cation either as an oxocarbenium or an aminocarbenium species: reactive intermediates that are capable of inducing subsequent transformations. In contrast to those initiated by epoxide opening, this type of reaction can take place either intermolecularly or intramolecularly. For the intramolecular cases, one advantage of this type of reaction is that carbocyclic or heterocyclic rings with an oxygen or nitrogen atom can be formed selectively, critically with proper placement of the heteroatom. Generally, such cation-initiated domino reactions involving a ring-closure procedure can be terminated by a nucleophile or a rearrangement process. The latter variant is now broadly known as the Prins–pinacol rearrangement.[‌84‌,‌85‌] Despite the broad application of this type of transformation, the corresponding enantioselective versions are still rare.

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References