Pericydic Reactions in Domino Processes

This deeper understanding (together with its impact on thermal vs photochemical reactions and the respective issues of stereoselectivity) paved the way to a plethora of 

Domino Reactions Concepts for Efficient Organic Synthetis, First Edition. Edited by Lutz F. Tietze. 

Heteroaromatic motifs are not the only accessible products of a cycloaddition/cycloreversion strategy. Cleverly shaped six-membered dienes with an intrinsic leaving group might also act as precursors for phenyl moieties. A definitely irreversible cycloreversion tailors this route for the integration of arenes into strained scaffolds. Beaudry and co workers [12] embarked on the synthesis of the conforma-tionally chiral macrocyclic natural product cavicularin. A vinyl sulfone moiety, acting as an alkyne equivalent, underwent a Diels-Alder reaction with a neighboring 

A contribution to the synthesis of oxoindoles equipped with quaternary stereocenters of high stereochemical purity was made by Smith et al. [15] in 2009. Nitrones 31 derived from Garner s aldehyde cycloadd readily to ketenes 32, a process that intensifies its asymmetric induction with increasing size of the protecting group (PG). An initially proposed ionic addition to the quaternary carbon of the ketene was subsequently mled out through computational methods [16]. The weak N-O 

Doyle and coworkers [19] presented an elaborate mechanism for their formation of tricychc heterocycles, although stiU in a more or less speculative state. Treating both reactants with an appropriate Rh catalyst transforms a diazo compound into 46. Presumably, the vinylogous double bond now undergoes an electronic activation, which tailors it for a cycloaddition with nitrone 45 furnishing exclusively 

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