Silyl enol ethers aziridination

Che et al. have reported that chiral Ru11(salen)s (54a) and (54b) are efficient catalysts for aziridination of alkenes (up to 83% ee) and amidation of silyl enol ethers (up to 97% ee), respectively (Scheme 39).163... 

The nitrido complex was applied to the direct asymmetric animation with a silyl enol ether as a substrate. Although several examples for achiral aminations of silyl enol ethers have been reported [32], an asymmetric version of reagent-controlled reaction has not appeared except for the one recent example [33] and the diastereoselective reactions with silyl enol ethers having a chiral auxiliary [34], The amination, which is presumed to take place via an aziridine intermediate [5g, lid,32], proceeded smoothly to give the A-tosylated a-aminoketone in 76% yield with 48% ee. When the same silyl enol ether was treated with complex 15 under Carreira s condition, the TV-trifluoroacetylated a-aminoketone was obtained in 58 % yield with 79 % ee (Scheme 24). 

Copper complexes derived from bis(-2,6-dichlorophenyle-dene)-( 15,25)-1,2-diaminocyclohexane (11) catalyze various reactions such as Diels-Alder reaction, aziridination (eq 20), cyclopropanation, and silyl enol ether addition to pyruvate esters. Although the scope of these reactions may be sometimes limited, enantioselectivities are generally high. The same complex (with copper(I) salts) catalyzes the asymmetric insertion of silicon- hydrogen bond into carbenoids. ... 

Kobayashi et al. found that lanthanide triflates were excellent catalysts for activation of C-N double bonds —activation by other Lewis acids required more than stoichiometric amounts of the acids. Examples were aza Diels-Alder reactions, the Man-nich-type reaction of A-(a-aminoalkyl)benzotriazoles with silyl enol ethers, the 1,3-dipolar cycloaddition of nitrones to alkenes, the 1,2-cycloaddition of diazoesters to imines, and the nucleophilic addition reactions to imines [24], These reactions are efficiently catalyzed by Yb(OTf)3. The arylimines reacted with Danishefsky s diene to give the dihydropyridones (Eq. 14) [25,26], The arylimines acted as the azadienes when reacted with cyclopentadiene, vinyl ethers or vinyl thioethers, providing the tet-rahydroquinolines (Eq. 15). Silyl enol ethers derived from esters, ketones, and thio-esters reacted with N-(a-aminoalkyl)benzotriazoles to give the /5-amino carbonyl compounds (Eq. 16) [27]. The diastereoselectivity was independent of the geometry of the silyl enol ethers, and favored the anti products. Nitrones, prepared in situ from aldehydes and N-substituted hydroxylamines, added to alkenes to afford isoxazoli-dines (Eq. 17) [28]. Addition of diazoesters to imines afforded CK-aziridines as the major products (Eq. 18) [29]. In all the reactions the imines could be generated in situ and the three-component coupling reactions proceeded smoothly in one pot. 

Aziridination.2 Aziridination of alkcncs can be effected with this nitrcnc precursor when catalyzed by various Cu(l) and Cu(ll) catalysts, particularly Cu(CHiCN)4004 and Cu(acac)2 in yields of 55-95%. Note that aziridination of a silyl enol ether provides an... 

The aziridination and amidation reactions of imidoiodanes can be efficiently catalyzed by Rh(II) complexes [810-815]. Dirhodium(II) tetrakis[Al-tetrafluorophthaloyl-(S)-tcrt-leucinate], Rh2(S-TFPTTL)4, has been found to be an exceptionally efficient catalyst for enantioselective aminations of silyl enol ethers 661 with imidoiodane 662 to afford a-amido ketones 663 in high yields and with enantioselectivities of up to 95% ee (Scheme 3.265). The effectiveness of this catalytic protocol has been demonstrated by an asymmetric formal synthesis of (-)-metazocine [810]. This catalyst has also been used for the asymmetric synthesis of phenylglycine derivatives by enantioselective amidation of silylketene acetals with PhINTs [811]. 

Different from their previous reports, Hashimoto and co-workers developed a novel reaction in 2009. They found that allylic C—H bond amina-tion reaction occurs when silyl enol ether 120 derived from cyclohexanone is used. This interesting insertion reaction is ascribed to the fact that silyl enol ether 120 can just be -shaped. On the other hand, when Z-shaped silyl enol ethers 118 were employed (Scheme 1.43, top), the aziridination reactions occurred under similar conditions. After treating with trifluoroacetic acid, the a-aminated carbonyl products 119 were obtained in high levels of enan-tioselectivity. Starting from the p-aminated carbonyl compound 121, they accomplished the formal synthesis of (-)-pancracine (Scheme 1.43, bottom). 

Fe(OTf)2-catalyzed aziridination of enol silyl ethers with PhlNTs followed by ring opening led to a-N-tosylamido ketones in good yields (Scheme 27) [81]. With silyl ketene ketal (R = OMe) as substrate, the N-tosyl-protected amino acid ester was obtained in 50% yield. In contrast, the copper (I) salt CuClOq was found not effective for this substrate [82]. 

Nitrosolysis of camphor ethyl acetal with ethanolic ethyl nitrite in sulphur dioxide yields the orthoester oxime (205) which is rapidly dehydrated by excess acetal to the orthoester nitrile which then reacts with sulphur dioxide to form the ester nitrile and diethyl sulphite.Further papers in this section include the full paper on ozonolysis of silyl ethers (Vol. 5, p. 33), another synthesis of camphor-enol trimethylsilyl ether (cf. Vol. 6, p. 41)/°° the conversion of camphor oxime with Grignard reagents into the corresponding imine with no aziridine formation/° the preparation of (206) by treating bornylene with trichloroacetyl isocyanate/ the oxidation of thiocam-phor to the 5-oxide and alkylation in the presence of thallium(i) ethoxide to a/S-unsaturated sulphoxides/ and the free-radical C-3 alkylation of camphor with alkenes. " ... 

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