- Intramolecular Addition of Nucleophilic Carbenes to Acceptor-Substituted Alkenyl Groups: Synthesis and Transformation of Homobenzofurans and Synthesis of a Homoindole
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The intramolecular addition of unsaturated alkoxycarbenes leads in high yields and diastereoselectively to fused cyclopropanes (Scheme 1).Reaction of the halodiazirines 2, 10, 11, and 20 with the unsaturated phenolates 1, 8, and 9 yielded intermediate alkoxydiazirines, and hence the homobenzofurans 5, 12-16, 22, and 26 (Scheme 2).The intermediate alkoxydiazirine 25 was isolated at low temperature (Scheme 3).An equilibrium between the cyclopropane derivatives 12 and 27, and 14 and 28 was established at 120 deg C.At 200 deg C, 12 rearranged to the chromene 29, by disrotatory opening of the cyclopropane ring, followed by electrocyclization.Hydrogenation of 29 gave the (all-cis)-chroman 32 (Scheme 4).The homoindole 35 was obtained in good yields, presumably by an SRN1 reaction from 34 and 10 (Scheme 5).
- Li, Chunbao,Vasella, Andrea
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p. 197 - 210
(2007/10/02)
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- SRN1 Reactions of Arylhalodiazirines with Azide Ion
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(m-(Trifluoromethyl)phenyl)bromodiazirine, 10, reacts with 15N terminally labeled sodium azide in dimethyl sulfoxide to give m-(trifluoromethyl)benzonitrile which, in all cases, contains 15N incorporation.The largest amount of label incorporation (42 percent) and the fastest rate, is observed when the reaction is carried out in room light.The smallest amount of label incorporation (11 percent), and the slowest reaction, is observed when the reaction is carried out in the dark and a trace of the free radical, galvinoxyl, is added.The reaction in the light is proposed to occur mainly via the SRN1 chain process.The intermediate C-azidodiazirine substitution product is not observed, but presumably rapidly loses 2 mol of nitrogen to give the nitrile product. (p-Nitrophenyl)bromodiazirine, 20, can also react with azide ion via an analogous SRN1 process, and the reaction is more facile than that of 10.Label incorporation from 15N-labeled sodium azide is substantial (47.3 percent) and is in agreement with the proposed SRN1 process.A variety of arylchlorodiazirines, substituted with electron-deficient aromatic groups, also react with azide ion in room light, to give nitriles via C-azidodiazirines, which lose molecular nitrogen.Evidence for the proposed SRN1 process includes initiation of the reaction by exposure to room light, initiation by the addition of the sodium salt of 2-nitropropane or sodium thiophenoxide, and inhibition of the reaction by the addition of galvinoxyl.In the case of these arylchlorodiazirines, reaction with 15N terminally labeled sodium azide led to 15N label incorporation approaching the maximum amount possible for a reaction proceeding exclusively via C-azidodiazirines.These studies show the propensity for arylhalodiazirines to undergo reaction initiated by electron-transfer processes.
- Creary, Xavier,Sky, Anthony F.,Phillips, Gillian
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p. 2005 - 2011
(2007/10/02)
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