Alkenes dipolarophile/dipole relative reactivity

Cycloaddition with nitrile oxides occur with compounds of practically any type with a C=C bond alkenes and cycloalkenes, their functional derivatives, dienes and trienes with isolated, conjugated or cumulated double bonds, some aromatic compounds, unsaturated and aromatic heterocycles, and fullerenes. The content of this subsection is classified according to the mentioned types of dipolarophiles. Problems of relative reactivities of dienophiles and dipoles, regio- and stereoselectivity of nitrile oxide cycloadditions were considered in detail by Jaeger and... 

The many successful applications of nitrile oxide cycloadditions in synthesis are intimately linked with theory, both the simple FMO variety as well as the more sophisticated ab initio treatment, where the work of Sustmann and subsequently of Houk and his group has been seminal. We, the practitioners, have thus been supplied with a consistent view on the nature of 1,3-dipoles, their reactivity toward dipolarophiles, and the origin and interpretation of stereoselectivity of cycloaddition chemistry. It is of course desirable that our understanding of the relative reactivities of alkenes as well as of many 1,3-dipoles would be also improved, thereby leading to simple, extended recipes for the chemist practicing synthetics. We hope that this account will stimulate further advances in this field of cycloaddition chemistry and promote further uses of nitrile oxides in organic synthesis. 

Intermolecular and intramolecular [3+2] cycloaddition reactions are among the most efficient and tvidely used procedures for synthesis of five-membered heterocycles. The reactive partners in these reactions are 1,3-dipoles and dipolarophiles such as alkenes and alkynes. 1,3-Dipoles vary in stability some can be isolated and stored, others are relatively stable, but they are usually employed immediately. Others are so unstable that they have to be generated and reacted in situ. There are tv ro general classes of dipole, often referred to as sp (Fig. 11.1) and sp -hybridized dipoles (Fig. 11.2). 

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