Cycloaddition to 1,3-Dienes

By analogy with carbenes, nitrenes undergo exclusive 1,2-addition to 1,3-dienes to give vinylaziridines, which on heating are transformed into dihydropyrroles. The reaction is known for various nitrenes, including ethoxycarbonylnitrene and 

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On a first, very broad, approximation singlet oxygen behaves somehow like ethylene. Three types of reactions of 102 are usually observed and have been utilized in organic synthesis 606 608) a) the Diels-Alder like cycloaddition to dienes (6.1) b) the ene reaction with olefins (6.2) and c) cycloaddition to activated double bonds (6.3). 

The most powerful dienophile is singlet oxygen, produced by the dye-sensitized irradiation of oxygen. Its cycloaddition to dienes to give ewrfo-peroxides (equation 86) has long been known76. 

In a similar reaction, 1,2-dibromocyclopropene may be prepared, characterized by NMR and trapped in high yield by [4 + 2]-cycloaddition to dienes (93% with DPIBF) while reaction of the tribromide with butyllithium leads to debromination127 ... 

The ene reaction of an azodicarboxylate ester was first observed in 196218-19 as a process competing with cycloaddition to dienes, but little additional work has been done on the ene reaction with simple alkenes. An elegant study in 1976 provided evidence for a concerted, suprafacial reaction between dimethyl azodicarboxylate and (S)-(Z)-l-deutero-4-methyl-l-phenyl-2-pentene (15) based on the direction and high level of chirality transfer observed20. 

Fulvenes, like their trpericyclic reactions. A reasonably well-defined reactivity profile of these systems has emerged as the result of extensive scrutiny of the cycloaddition behavior of the fulvene nucleus. To a large extent, fulvenes undergo concerted cycloadditions to dienes as either the 6ir or lit participant and the factors governing which of these reactivities is expressed in a particular circumstance has been elucidated employing fiontier molecular orbital considerations. ... 

Extension of diis methodology to nitrogenous compounds (Scheme 53) has been implemented via azide cycloadditions to dienes as a facile means of synthesis of functionalized pyrrolizidines. Recently a [2 -I- 3] methodology was developed (Scheme 54) that promises to have wide tqrplicability in the synthesis of cyclopentanoids, bridged systems and dihydrofurans. ... 

While cumulene V might evolve directly into dimethylfiimarate derivative III by proton transfer, alternatively, it might evolve into cyclobutene VI, whereby the desired C-6 methyl acetate unit is expediently formed. Such a structure has very little chance to survive in a hot reaction medium and three decomposition reactions are likely to take place (1) return to starting materials (2) a metathesis-type retro(2-l-2]cycloaddition to diene VII, something that finds... 

A more recent variation of the general procedure described in the previous section involves the use of adducts of l-bromo-2-chlorocyclopropene as substrates for the double elimination reaction.Thus, l/f-cyclopropa[6]phenanthrene (4) was obtained in 89% yield in the final step of a sequence that included cycloaddition to diene 1 followed by aromatization. ... 

Aromatic diazonium salts undergo cycloaddition to dienes to produce N-substituted 1,6-dihydropyridazines 53 [Eq. (8)]. 

The double bonds also undergo cycloadditions to dienes (Section 14-8). The initial cycloadduct to 1,3-butadiene tautomerizes with acid to the aromatic system. 

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