Reactions of N-O Systems

Terrier et al. have widely described Bfxs 4-nitro-substituted participating in a series of Diels-Alder processes. Bfx 4-nitro-substituted system could participate as diene, C = C - C = C system, or heterodiene, C = C - NO2 system, in an inverse electron demand reaction [62,63] or as dienophile, C = C or N = O systems, in a normal electron demand reaction [64-68]. Fxs have been reported as 1,3-dipole through the substructure C = - 0 reacting with... 

Beyond palladium, it has recently been shown that isoelectronic metal complexes based on nickel and platinum are active catalysts for diyne reductive cyclization. While the stoichiometric reaction of nickel(O) complexes with non-conjugated diynes represents a robust area of research,8 only one example of nickel-catalyzed diyne reductive cyclization, which involves the hydrosilylative cyclization of 1,7-diynes to afford 1,2-dialkylidenecyclohexanes appears in the literature.7 The reductive cyclization of unsubstituted 1,7-diyne 53a illustrates the ability of this catalyst system to deliver cyclic Z-vinylsilanes in good yield with excellent control of alkene geometry. Cationic platinum catalysts, generated in situ from (phen)Pt(Me)2 and B(C6F5)3, are also excellent catalysts for highly Z-selective reductive cyclization of 1,6-diynes, as demonstrated by the cyclization of 1,6-diyne 54a.72 The related platinum bis(imine) complex [PhN=C(Me)C(Me)N=Ph]2Pt(Me)2 also catalyzes diyne hydrosilylation-cyclization (Scheme 35).72a... 

Aromatization of hydrocarbons with more than six carbon atoms is thermodynamically even more favorable than the reaction of n-hexane 28). These hydrocarbons offer more than one way of cyclization, for example, n-octane may give either o-xylene or ethylbenzene. -Nonane can even give bicyclic products (indane system) (72). 

The rate constants for the reaction of N-dodecyl-3-carbamoyl-pyridinlum ion with cyanide in both cationic and nonionic o/w microemulsions have been measured as a function of phase volume. Added salt has no effect in the cationic system, but the rate constants in the nonionic system depend upon ionic strength as would be expected for a reaction between two ions. In order to compare the two microemulsions, the ionic strength in the reaction region has been estimated using thicknesses of 2-4A. The former produces values of the effective surface potential which yield... 

It is well known that trivalent carbenium ions play an important role in electrophilic reactions of 7t- and -donors systems. Similarly, pentacoordinate carbonium ions are the key to electrophilic reactions of o-donor systems (single bonds). The ability of single bonds to act as o-donors lies in their ability to form carbonium ions via delocalized two-electron, three-center (2e-3c) bond formation. Consequently, there seems to be in principle no difference between the electrophilic reactions of n- and O-bonds except that the former react more easily even with weak electrophiles, whereas the latter necessitate more severe conditions. 

The synthesis of l-azabicyclo[4.n.O] systems 31 has also been carried out by using a similar substitution between heteroaromatic rings such as furan and the N-acyliminium ion as the key reaction 20). 

Only a limited number of X = Y species undergo ene reactions with formation of a C-N bond, and practical processes appear limited to R —N = N —R and R —N = o systems. 

Data on the elementary steps in the H—N—O system is much less plentiful than in the case of the hydrogen—oxygen system, and for many reactions there is no reliable measurement available. Table 49 summarizes the data which are available. 

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