[Development of domino reactions based on skeletal rearrangement]

Domino reactions, which enable formations of several chemical bonds and multi-step transformation in one-pot process, have received much attention as an efficient synthetic methodology to preserve chemists from time-consuming purification protocols and protection-deprotection procedures. Furthermore, the domino processes containing skeletal rearrangement have been utilized for constructions of complex molecules because of their potential that they could afford entirely different valuable structures from readily available simple substrates. We recently developed novel domino reactions including ring enlargement process, which could afford biologically important cyclopentanones and nitrogen heterocycles. In this review, we will describe 1) a novel type of palladium-catalyzed domino insertion-ring expansion reaction of dienylcyclobutanols, which could enable a stereospecific synthesis of (Z)-2-(3-aryl-1-propenyl)cyclopentanones, 2) ruthenium-catalyzed domino ring expansion-insertion reaction of 1-acetylenylcyclobutanols for a construction of 2-alkylidenecyclopentanones, and 3) DIBALH-mediated reductive ring expansion reaction of oximes and studies on the reaction mechanisms. The rationales for the observed stereoselectivities in each reaction are also discussed.