Alkenes nitrogen-functional

Oxaziridines unsubstituted at nitrogen as well as some iV-acylated oxaziridines offer synthetic potentialities due to their ability to transfer their nitrogen function to nucleophiles (Section 5.08.3.1.4). The simplicity of preparation of some aziridines from alkenes and the Spiro oxaziridine (S2) equals the simplicity of epoxidation. Aziridine (299), for example, is obtained by simple heating of indene with (52) in toluene (74KGS1629). 

Intramolecular 1,3-dipolar cycloadditions have proven to be especially use fid in synthesis. The addition of nitrones to alkenes serves both to form a carbon-carbon bond and to introduce oxygen and nitrogen functionality.86 Entry 7 in Scheme 6.5 is an example. The nitrone B is generated by condensation of the aldehyde group with 7V-methylhydrox-ylamine and then goes on to product by intramolecular cycloaddition. 

But due to the importance of nitrogen functional groups, the addition reactions of selenium electrophiles to alkenes using nitrogen nucleophiles represent another synthetically relevant process. Nitriles have been used as versatile... 

Thermolysis of pyrazolines was also used for aminocyclopropane synthesis. The corresponding starting materials were obtained from diazomethane and an alkene bearing a suitable nitrogen functional group, e.g. an amido or azido moiety. 

Intramolecular nitrone cycloadditions often require higher temperatures as nitrones react more sluggishly with alkenes than do nitrile oxides and the products contain a substituent on nitrogen which may not be desirable. Conspicuously absent among various nitrones employed earlier have been NH nitrones, which are tautomers of the more stable oximes. However, Grigg et al. [58 a] and Padwa and Norman [58b] have demonstrated that under certain conditions oximes can undergo addition to electron deficient olefins as Michael acceptors, followed by cycloadditions to multiple bonds. We found that intramolecular oxime-olefin cycloaddition (lOOC) can occur thermally via an H-nitrone and lead to stereospecific introduction of two or more stereocenters. This is an excellent procedure for the stereoselective introduction of amino alcohol functionality via N-0 bond cleavage. 

A novel and highly efficient synthesis of 1,1-diiodo-, 1,1-dibromo-, and mixed (Z)- or ( )-1-iodo-l-bromo-l-alkenes using the 1,1-heterobimetallic reagents obtained by hydrozirconation of stannylacetylenes has also been described [155], The hydrozirconation and halo-genolysis steps were carried out at room temperature in THF under a nitrogen atmosphere. It is noteworthy that the developed route is compatible with various functionalities... 

The products of nitrone-alkene cycloadditions are isoxazolines, and the oxygen-nitrogen bond can be cleaved by reduction, leaving both an amino and a hydroxy function in place. 

Elsewhere, Heaney et al. (313-315) found that alkenyloximes (e.g., 285), may react in a number of ways including formation of cyclic nitrones by the 1,3-APT reaction (Scheme 1.60). The benzodiazepinone nitrones (286) formed by the intramolecular 1,3-APT will undergo an intermolecular dipolar cycloaddition reaction with an external dipolarophile to afford five,seven,six-membered tricyclic adducts (287). Alternatively, the oximes may equilibrate to the corresponding N—H nitrones (288) and undergo intramolecular cycloaddition with the alkenyl function to afford five,six,six-membered tricyclic isoxazolidine adducts (289, R = H see also Section 1.11.2). In the presence of an electron-deficient alkene such as methyl vinyl ketone, the nitrogen of oxime 285 may be alkylated via the acyclic version of the 1,3-APT reaction and thus afford the N-alkylated nitrone 290 and the corresponding adduct 291. In more recent work, they prepared the related pyrimidodiazepine N-oxides by oxime-alkene cyclization for subsequent cycloaddition reactions (316). Related nitrones have been prepared by a number of workers by the more familiar route of condensation with alkylhydroxylamines (Scheme 1.67, Section 1.11.3). 

Aside from the relatively trivial conversions of nitronates to the corresponding oxime and carbonyl compounds (10,11), the chemistry of nitronates remained relatively unexplored for much of the early 1900s. However, in 1964, Tartakovskii et al. (12) demonstrated that alkyl nitronate esters were competent partners in the newly discovered class of dipolar cycloadditions with alkenes (Scheme 2.1). Both cyclic and acyclic nitronates participated, thus providing a new functional group were the nitrogen atom existed at the center of an acetal (13). These compounds were subsequently referred to as nitroso acetals (14) or nitrosals (15). 

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