Retro-cycloaddition reactions

N,N -linked synthesis, 5, 269 6,6 -Biazulenes synthesis, 1, All Bibenzimidazolyls 3-oxides synthesis, 5, 412 1,1 - Bibenzimidazolyls synthesis, 5, 459 2,2 -Bibenzo[b]selenienyl synthesis, 4, 947 2,2 -Bibenzothiazolyl reduction, 6, 260 4,4 -Bichromenyl synthesis, 3, 743 Bicyclo[n. 1.0]alkanes retro-cycloaddition reactions, 1, 668 Bicyclo[5.3.0]decane synthesis, 1, 420 Bicyclo[4.1,0]diheteroheptanes synthesis, 3, 977... 

Lukoyanova, O., Cardona, C.M., Altable, M. eta/. (2006) Selective electrochemical retro-cycloaddition reaction of pyrrolidinofullerenes. Angewandte Chemie International Edition, 45, 7430-7433. 

It appears likely that transient metallacyclobutanes are involved in a variety of organic reactions which are catalyzed by transition metal complexes. Thus, cycloadditions of activated alkenes to strained hydrocarbons such as quadricyclane and bicyclo[2.1.0]pentane are catalyzed by complexes such as Ni(CH2=CHCN)2 and probably involve initial formation of a nickelacyclobutane (Scheme 2) (79MI12200). The nature of the organometallic intermediates in related metal-catalyzed rearrangements (72JA7757) and retro-cycloaddition reactions (76JA6057) of cyclopropanoid hydrocarbons, e.g. bicyclo[n.l.O]alkanes, has been discussed. 

Presumably in the first step the l-sila-2-oxa-4-azetane (type A molecule) is formed. By means of a [2+2] retro-cycloaddition reaction intermediate A yields PhN=CH2 and (2-Me2NCH2C6H4)-(CH2=CH)Si=0 (Scheme 1). The latter is not stable under the reaction conditions and 7 is formed by trimerization of PhN=CH2, while oligomerization of (2-Me2NCH2C6H4)(CH2=CH)Si=0 yields the siloxane 3. 

Tliree general methods have been used for the preparation of cyclobutadienes, namely dehalogenation of 3,4-dihalogenocyclobutenes, oxidation of cyclobutadiene metal complexes and photochemical retro--cycloaddition reactions. 

Most modem syntheses of 1,2,4-oxadiazoles are classifiable as belonging to one of the two classical strategies described above (Schemes 1 and 2). Protected precursors are sometimes used, particularly when the lateral moiety in the final oxadiazole ring is sensitive to the reaction conditions (2012JOC4832). In some cases, alternative methodologies have been developed to generate particularly reactive precursors in situ for example, a photoinduced retro-cycloaddition reaction of acylamino furazan 8... 

Similarly, in cycloreversion or retro cycloaddition reactions, c-bonds take part in bond reorganization process. The cycloreversion of Diels—Alder reaction [7r" s + TT s] and of [tt s + tt s] cycloaddition may be designated as [cr s + CT s + TT s] and [ct s + c s] cycloaddition, respectively. In suprafacial cycloreversion, either retention or inversion at both the ends of other hand, antarafacial process provides retention at one end and inversion at the other end of the a-bond (Figure 4.3). 

The 1,3-dipolar retro-cycloaddition reaction turned out to be quite general and occurs in the presence of an excess of a highly efficient dipolarophile (30 equiv), such as maleic anhydride, which traps the corresponding ylide resulting from the thermal retro-cycloaddition. In the absence of the metal salts, the reaction yields depend on the refluxing temperature, the pyrrolidine substitution pattern [unsubstituted (16a), monosubstituted (16b, c, e), and disubstituted (16d)] (Scheme 34.6), and the nature of the substituents on the pyrrolidine ring, which influence the stability of the thermally generated 1,3-dipole. 

Scheme 34.6 Retro-cycloaddition reaction of pyrrolidino[3,4 l,2][60]fullerenes (16a-e).

Scheme 34.7 Retro-cycloaddition reaction of higher and endohedral pyrrolidinofullerenes.

A very important characteristic of fulleropyrrolidines is high stability. Retro-cycloaddition reactions, although reported, have to be carried out under harsh conditions, such as high temperatures while trapping the ylide with a metal and a dipolarophile," or by microwave irradiation in ionic... 

---