Dienes aziridination

In some instances the vinyl azide does not undergo the conversion to the 2/f-azirine and instead yields a nitrene, which adds to alkenes and dienes. This is seen with the azide 653 which, on irradiation through Pyrex, affords the corresponding nitrene that adds to alkenes stereospecifically to yield aziridines. Stereo specific addition to dienes is exemplified by the irradiation of the quinone azide 654 in the presence of trans,trans-hQX3,-2,4-diene. Aziridines do not result from this process and instead the stereoisomeric indole derivatives 655 and 656 are obtained. This process has been developed as a route to... 

The formal 4 + 1-cycloaddition of conjugated dienes and nittene precursors, PhI=NR, in the presence of the active catalyst, [Cu(hfacac)2] (hfacac = 1,1,1,5,5,5-hexafluoroacetylacetonate), yielded 3-pyrrolines with a good to excellent stereo-selectivity. The cycloaddition proceeds through diene aziridination followed by ring expansion. The Ni(I)-catalysed 4 + 1-cycloaddition of methylene... 

A range of 3-pyrrolines could be synthesized from conjugated dienes with common nitrene precursors catalyzed by [Cufhfacaclj] via intermolecular [4h-1] cycloaddition. Good to excellent cisltmns selectivity could be obtained when 1,4-disubstituted dienes are used as substrates. The cis or trans preference depends on the nature of the substituents of the substrates. Mechanistic studies disclose that this transformation proceeds through diene aziridination and subsequent ring expansion. The [Cufhfacaclj] catalyst shows higher activity than other copper catalysts [41] (Scheme 8.17). 

Many a,/ -unsaturated keto steroids undergo conjugate addition and thereby provide a unique route to aziridines. Treatment of 3j5-hydroxypregna-5, 16-diene-20-one acetate (48) with methoxyl-or ethoxylamine in ethanol under... 

H -hydroxyandrost-5-en-3-one acetate and 4-methyl-6 -acetyI-H -hydroxyandrost-5-en-3-one acetate from 4-methylandrosta-3,5-diene-3,17-diol diacetate, 342 Preparation of aziridines... 

In 1995, aziridination with 1,3-dienes 10 by treatment with PhI=NTs 9 was developed (Scheme 2.4) [10] on the foundation of pioneering works by Jacobsen and Evans on copper-catalyzed asymmetric aziridination of isolated alkenes [11]. 

Scheme 2.4 Aziridination of dienes with [(N-tosyl) iminojphenyliodinane 9.

Scheme 2.5) was recently reported by Komatsu, Minakata, and coworkers [12]. The reaction with the (i ,i )-complex 12 provided the first reagent-controlled asymmetric aziridination of conjugated dienes, although enantioselectivities were only low to moderate (20-40% ee). 

Sharpless asymmetric dihydroxylation procedure was applied to the synthesis of the side chain of azinomycin A (equation 26)43. Horner-Emmons condensation of phospho-nate 36 with a /J-aziridine substituted acrolein afforded dehydroamino acid diene 37. Treatment of the diene with catalytic amounts of an osmium reagent and dihydroquini-dine (DHQD) p-chlorobenzoate resulted in asymmetric dihydroxylation, producing diol 38. Diol 38 was further converted to the naphthyl ester. 

Interesting rearrangements proceed upon refluxing the azido diene 105 in benzene solution and form 61% of the vinylaziridine 106 as a mixture of diastereoisomers and the vinylogous urethane 108 (28%) (equation 37)53. It was shown that the process 106 - 108 occurs entirely at elevated temperature (refluxing xylene, ca 140 °C). However, treatment of the aziridine 106 with p-toluenesulfonic acid in THF at room temperature gives rise to trans,trans-, 3-butadiene carboxylic ester 107 in 98%53. 

Ring closing metathesis mediated by Grubbs II catalyst in a type c ring construction process has been used to access stereoisomeric 1,2-disubstituted tetrahydroazepine-3-ol derivatives preparation of the required diene precursor started from an optically pure substituted aziridine carboxylate ester <2007T3321>. 

This nitrene-addition approach was used by Knight to synthesize vinyl aziridines from 1,3-dienes using PhI=NTs and a copper catalyst. The more electron-rich double bond is selectively transformed in most cases. When the electronic difference is negligible the regioselectivity is then determined by steric hindrance. A mixture of cis and tram isomers is usually obtained [95SL949],... 

OT w-2,6-Diaryl-4-piperidones were produced in a [4+2] cycloaddition reaction using aryl-iV-allylimines and a diene in the presence of Cu(OTf)2 in high yield and de (>99%) (Scheme 87) <2004TL4357>. Reaction of imines with /3,7-unsaturated a-bromoketenes yields dihydro-2-pyridones some of which were reacted with allylamines producing aziridines with 99% de in generally high yield <2004TL5031>. 

REACTIVITY OF IODINE-NITROGEN YLIDES 10.3.1 Aziridination of alkanes and dienes... 

For the aziridination of 1,3-dienes, copper catalysis gave better yields of A-tosyl-2-alkenyl aziridines with 1,3-cyclooctadiene, 1,4-addition occurred exclusively (50%) [46]. Good results were also obtained on rhodium catalysed decomposition of PhI=NNs (Ns = p-nitrophenylsulphonyl) with some alkenes the aziridination was stereospecific, whereas with chiral catalysts asymmetric induction (up to 73% ee) was achieved. However, cyclohexene gave predominantly (70%) a product derived from nitrene insertion into an allylic carbon-hydrogen bond [47]. 

Scheme 22. Comparison of aziridination of 1,3-diene with nitrido complex versus PhI=NTs.

The achiral aziridination with the racemic nitrido complex 15 was successfully applied to a wide range of 1,3-dienes (Table 6.6). Cyclic conjugated dienes were smoothly aziridinated under mild conditions with no [4+1] adducts. Among these, cyclohexadiene and cycloheptadiene reacted with the complex in good yields. When the unsymmetrical dienes were employed in the reaction, the aziridi-nations of isoprene and trans-1,3-hexadiene proceeded, giving two regioisomers in 70 30 and 94 6, respectively. The major isomers in both reactions were formed by the aziridination of the less substituted olefins of the 1,3-dienes. 

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