Heterocyclicmoleculesplayasigni?cantroleinlifeprocessesandhaveplayed a major rolein industrial developments of the last century, for instance in the ?eld of dyes, pharmaceuticals, pesticides, polymers etc. They comprise not onlysomeofthemostinterestingandbiologicallyimportantnaturalproducts like alkaloids, carbohydrates, nucleic acids, and antibiotics but include many practical drugs and a large segment of known synthetic organic compounds. Hencescientistshavedevotedagreatamountofeffortto?ndoptimalsynthetic approachesto a variety ofheterocyclic compounds. Amongthemostsuccessfulandselectivesyntheticprocessesarecycload- tionreactions,since theyinvolvesimultaneous orsequential formationoftwo or more bonds often with a high degree of stereoselectivity and regiosel- tivity.Forinstance, 1,3 dipolar cycloadditions,whichare electronicallyequ- alent to Diels-Alder reactions, are among the most-common 5-membered ring-forming systems. In addition they usually proceed with a high degree of stereo-andregio-control.Itistherefore,notsurprising thatsynthesisofmany important classes ofheterocycles, including thoseof useful biologicallyactive molecules, have utilized cycloadditionsteps intheirformation.Furthermore, many heterocycles serve as intermediates in the synthesis of polyfunctional molecules. Volume I of "Synthesis of Heterocycles via Cycloadditions" featured ?ve chapters onthe followingtopics: - Isoxazolines fromNitroCompounds: Synthesis and Applications; - Cycloaddition Reactions of Azides Including Bioconjugation; - Enantioselective Cycloadditions ofAzomethine Ylides; - Heterocyclesby Cycloadditions of CarbonylYlides Generated fromDiazo Ketones; - HeterocyclesfromUnsaturated Phosphorus Ylides. In this volume we present four selected contributions by well-known authors, each an authority in his ?eld. The ?rst chapter is devoted to the use of oximes in cycloadditions which leads to formationof isoxazolines and isoxazolidines and from there to synthesis of macrolides like amphotericin and of other natural products and bioactive molecules. Furthermore, 4+2 cycloadditions of nitrosoalkenes are also included. This chapter complements the one in the X Preface previous volume which discussed access to isoxazolines via nitroalkanes.