Aziridination, olefins

Johnston reported TfOH promoted addition of alkyl azides to a,P-unsaturated carbonyl compounds [30]. The corresponding aziridines were obtained from a,P-unsaturated ketones in good yield under relatively mild and non-redox conditions (Table 2.18). Furthermore, formal anti-P-amino-a-hydroxylation occurred from a,P-unsaturated imide with high regio- and stereoselectivity (Table 2.19). 

Reversal of Chemoselectivity in Diels-Alder Reactions In 2003, Yamamoto et al found unusual reversal of chemoselectivity in Diels-Alder reaction catalyzed by 

COEt f Diene (1 equiv) Diels-Alder Adduct Diels-Alder Adduct 

Entry Diene Conditions Catalyst (mol%) Yield (%), Ratio of A B 

Esterification In 2000, Tanabe et al. reported that diphenylammonium triflate ([Ph2NH3] [OTf 1 10mol%) catalyzed the ester condensation reaction of 

---

Stance, although Mn(TPP)Cl-catalyzed reaction of 19 with styrene affords aziridine derivative in 80% yield (Eq. 13), significantly lower yields are obtained with other olefins. Allylic insertion by the metal nitrenoid is frequently the major side reaction encountered during olefin aziridination (88TL1927) (Eq. 14). 

Pancralistatin, [29], The first asymmetric total synthesis of (+)-pancratistatin (94) was reported by Hudlicky 130,26], Thus the bromo olefin 114 (Scheme 15), obtained by a-addition of copper nitrenoid generated from (N-tosyiimino) phenyliodinane to 45, was debrominated to the olefinic aziridine 117. The latter underwent Irons 1,2-ring opening with diarylcyancuprate... 

Scheme 6.2. Olefin aziridination using chloramine-T as a nitrene source.

TABLE 6.1. Substrate Scope for Olefin Aziridination by Silver-Terpyridine Catalyst... 

Scheme 6.3. Silver-terpyridine catalyst can catalyze olefin aziridination using an in situ prepared nitrene.

After successful application of the silver catalyst shown in olefin aziridination (Section 6.1.1), He and coworkers showed that intramolecular amidation was possible with both hydrocarbon-tethered carbamates and sulfamate esters.24 They found that only the Bu3tpy silver complex could catalyze efficient intramolecular amidation, while other pyridine ligands gave either dramatically lower yields or complicated product mixtures. In an interesting control study, both copper and gold were also tested in this reaction. Both the copper and gold Bu tpy complexes can mediate olefin aziridination, but only silver can catalyze intramolecular C-H amidation, indicating that the silver catalyst forms a more reactive metal nitrene intermediate. 

Olefin aziridination catalysts derived from other transition metals continue to be developed. Simple non-heme iron complexes have been reported to serve as effective... 

A more promising olefin aziridination protocol with silver in catalytic amounts was developed in 2003 (112). A novel Ag2(l) compound was prepared from the reaction of 1 equiv of different silver(l) salts and 1 equiv of 4,4, 4"-tri-ferf-butyl-2,2 6,2 -terpyridine(f-Bu3tpy)inMe3CN at room temperature (Fig. 19). 

Figure 20. Olefin aziridination with Phi — NTs utilizing the silver catalyst shown in Figure 19.

Siu, T. Yudin, A. K, Practical olefin aziridination with abroad substrate scope, J. Am. Chem. Soc. 2002,124, 530-531... 

Despite these significant advances, allylic C H insertion under these conditions remains problematic, with competing olefin aziridination often observed as the dominant reaction pathway (Scheme 12.5) [29]. 

It was recently demonstrated that 34 transfers its NH group to olefins. Aziridine 49 is obtained in 46% yield from a-methylstyrene 48 by 3 hours of heating with a solution of 34 in toluene. The same reaction was observed with styrene and its ring substitution products, indene, 1,1-diphenylethylene, and also norbornene and acrylonitrile. ... 

Scheme 18 The first example of an olefin aziridination reaction with a Tp CuL catalyst...

It is worth mentioning that mechanistic studies on the olefin aziridination reaction with TffML complexes have shown that this transformation occurs throughout a complex pathway (Scheme 20) that involves metallonitrene intermediates in the triplet state as well as both singlet and triplet reaction pathways, which intercross several times along the... 

Cu-promoted reaction and Cu-catalyzed C-H amination merit some analysis of the former process. From the standpoint of reaction utility, the work of Dauban and Dodd [31, 32] and, more recently, Lebel [33] has advanced Cu-catalyzed alkene aziridination to a state-of-the-art synthetic method. In particular, Dauban and Dodd have shown that pre-formation of sulfonyliodoimines is not required and that such species can be generated in situ from the corresponding sulfonamide and Phl=0. These conditions greatly expand the number and type of sulfonamide derivatives that will engage in olefin aziridination processes. 

On the development of copper-catalysed olefin aziridination, Evans et al. [36] reported oxidative amidine formation. Treatment of cyclohexene, a less reactive substrate towards... 

Evans,D.A., Eaul,M.M.and Bilodeau, M.T. (1994) Development ofthe copper-catalysed olefin aziridination reaction. Journal of the American Chemical Society, 116, 2742-2753. 

The diphenylphosphoryl azide (DPPA) (38) has been employed as a nitrene source in the presence of a cobalt(II) porphyrin [Co(Por)] system, catalyzing asymmetric olefin aziridination reactions (Scheme 11). iV-phosphorus-substituted aziridines (39) have been formed in these reactions in moderate to high yields and good enantioselectivities. 

---