2-Aminoallyl cations

Of the substituents considered in Figure 25, The amino group is the strongest re-donor and, not surprisingly, the a-aminocyclopropyl cation is more stable than the 2-aminoallyl cation by 23.4 kcal mof1 at the HF/6-31G(d)//HF/3-21G level of theory. This is in line with... 

The [4+3] cycloaddition between furan and amino-stabilized allyl cations has not been as actively studied. An intramolecular cycloaddition between a furan and a 2-aminoallyl cation, generated from methyleneaziridine under Lewis acid-promoted conditions, is shown in Equation (50) <2004AGE6517>. An AgBF4-promoted asymmetric intermolecular [4+3] cycloaddition of 2-aminoallyl cations, derived from chiral a-chloroimines, with furan to give cycloadducts of up to 60% ee was also reported <1997TL3353>. 

Y = pyrrolidino) with AgC104 or AgBp4 in THF or dichloromethane generates 2-aminoallyl cations (5f ... 

Ab initio calculations indicated that the cyclopropiminium ion is more stable than the 2-aminoallyl cation.As allyl cations can be generated from the reaction of allylic halides with silver salts, ° reactions of a-haloenamines with these salts have been investigated in order to increase the yield and chemoselectivity of the formation of bicyclo[3.1.0]hexan-6-one aminals. ° ... 

Dimethyl(succinimido)sulfonium fluorosulfate 2, easily prepared from /V-chlorosuccinimide (1), dimethyl sulfide, and methyl fluorosulfate, reacted with 1-dialkylaminocycloalkenes 3 to give fair yields of (2-dialkylaminocycloalk-l-enyl)dimethylsulfonium fluorosulfates 4 or their thermally rearranged allylic isomers 5.22 23 At elevated temperatures 4 or 5, respectively, reacted with nucleophiles Nu to give c -bicyclo[n.l.O]alkanes 8 or 9 via (Z,Z)-2-aminoallyl cation 6 or trans-bicyclo[n.l. 0]alkanes 12 via ( , Z)-2-aminoallyl cation 10, in fair to excellent yield.23 " 42 Normally, ra-annulated cyclopropylamines 8, resulting from kinetically preferred attack of... 

A related intermolecular [4-1-3] cycloaddition of a furan with 2-aminoallyl cations, generated from methyleneaziridines under Lewis acid conditions, was also developed. A representative example is shown below <04AG(E)6517>. 

Shipman and coworkers have shown that coordination of Bp3 OEt2 to 2-methylene aziridines (21) lead to an alternative precursor to 2-aminoallyl cations, which can be trapped with an appended 1,3-diene to effect an intramolecular [4 + 3] cycloaddition reaction that generates seven-membered ring systems such as (22) (Equation 16) [22]. 

An extensive review of the synthesis of a wide variety of five-membered heterocyclic compounds, via the formal 3-1-2-cycloaddition reactions of aziridines with alkenes, alkynes, nitriles, carbonyl groups, and heterocumulenes, has been presented." Supercritical CO2 has been used as the solvent in the formal 3-1-2-cycloaddition reactions of A-benzyl- and A-cyclohexyl-2-benzoyl-3-phenylaziridines with allenoates to yield pyrrole derivatives." The Lewis acid-catalysed intramolecular formal 3-1-2-cycloaddition reactions of 2-methyleneaziridines with tethered alkenes or alkynes (23) yielded cw-octahydrocyclopenta[c]pyrroles (24) after reductive workup. The reaction mechanism proceeds in a stepwise manner via a 2-aminoallyl cation (Scheme The Cu(I)/DTBM-Segphos-catalysed 1,3-dipolar cycloaddition reactions of a-silylimines and activated alkenes yielded highly enriched 5-unsubstituted a-quaternary proline cycloadducts with excellent diastereo- and enantio-selectivities (73-99% The... 

The preparation of aminocyclopropane derivatives from substituted chloroenamines showed some restrictions. The substituent influences both the energy difference between aminoallyl cation and cyclopropaniminium ion and a subsequent homoenamine ringopening. Thus, the stabilization of the positive charge in a dibenzotropylium species (237) may be the reason for the formation of 239 from 236 and nucleophiles like OH , HNMe2/AgN03 or RS" So far, only treatment of 236 with sodium borohydride led to aminocyclopropane compound 240 (Nu = H) (equation 56). 

CYCLOADDITION OF AMINOALLYL CATIONS WITH 1,3-DIENES 11-OXATRICYCLOl4.3.1.12>5]UNDEC-3-EN-10-ONE. 

Cha and coworkers have reported an enantioselective synthesis of (-t-)-cw-lauthisan 53 in which enzymatic desymmet-rization was used [33]. The researchers employed an allylic chloroenamine as a cation precursor and performed the cycloaddition on a multigram scale. They began by [4+3] cycloaddition of chloroenamine 44 with furan in the presence of silver cation to afford cycloadduct 47 in 72% yield (Scheme 19.18) [34]. Generation of the aminoallylic cation... 

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