1.3- dipole formation product ring systems

The rhodium( 11)-catalyzed formation of 1,3-dipoles has played a major role in facilitating the use of the dipolar cycloaddition reaction in modern organic synthesis. This is apparent from the increasing number of applications of this chemistry for the construction of heterocyclic and natural product ring systems. This chapter initially focuses on those aspects of rhodium(II) catalysis that control dipole formation and reactivity, and concludes with a sampling of the myriad examples that exist in the Hterature today. 

The rhodium-catalyzed formation of the above six membered 1,3-dipoles is involved in the construction of various other complex ring systems, including the oxatricyclo[6.3.1.0° °]dodecane core of komaroviquinone <2005OL3725>, the synthesis of tropolone natural products <19990L1933> and the cyclization of o-(l,6-enynyl)benzaldehydes, which leads to polycyclic ring systems seen in many natural products <2005CC4429>. 

Scheme 17.12. Stepwise decompositions of protonated Aspidosperma alkaloid occurring by either (a) stereochemical D ring cleavage yielding loss of acetamide neutral or (b) ion-dipole complex formation by A-benzyl bond cleavage of the protecting group of the indolic system decomposing into odd-electron product ions. (Adapted with permission from Ref 61.)...

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