Nucleophilic azide

SUBSTRATE-SPECIFIC REACTIONS OF DIBROMIDES OF a-ARYLI-DENE-BENZOCYCLANONES WITH AZIDE NUCLEOPHILE... 

Chalcone dibromides are advantageous intermediates for the preparation of various nitrogen-containing heterocycles (refs. 1-4). In the case of exocyclic a,P-unsaturated ketones, however, only few examples are known concerning the utilization of their dibromides for such purposes (ref. 5). Our aim was, therefore, the synthesis of the dibromides of various exocyclic a,P-unsaturated ketones (ref. 6) and to study their chemical transformations. In our present paper the reaction of such dibromides with azide nucleophile is reported. 

Quite analogous ring-closures occur when the 1-O-acetyl derivatives of the rhamnopyranose and talopyranose derivatives are treated with sodium azide in N,N-dimethylformamide. l-O-Acetyl-6-deoxy-2,3-0-isopropylidene-4-0-mesyl-a-L-mannopyranose is converted exclusively into l,4-anhydro-6-deoxy-2,3-0-isopropylidene-/3-L-talo-pyranose. In this instance, the azide nucleophile attacks the l-O-ace-tyl group, liberating an 0-1 oxide ion which reacts with inversion of C-4. The 4-epimeric, l-O-acetyl-6-deoxy-talose derivative gives 60% of the direct inversion product l,4-anhydro-6-deoxy-2,3-0-isopropyli-dene-a-L-mannopyranose, together with other products.50... 

Chemically, and in a somewhat analogous fashion to the tetrazole-norstatine libraries described earlier, the intermediate Ugi nitrilium ion may also be trapped by an azide nucleophile, generating racemic monocyclic tetrazoles. Workers at Amgen have reported utilizing this methodology for the generation of a 10000-... 

Several examples of reactions of allyl alcohols under Mitsunobu reaction conditions using diethyl azodicarboxylate (DEAD) and triphenyl phosphine giving allyl amines are known. An example is the reaction of the steroid 5 with azide nucleophiles under Mitsunobu reaction conditions, giving the corresponding azide 6 in 63 % yield (Eq. (3)) [5]. The reaction is regioselective with inversion of the configuration and no SN2/ substitution is observed. 

A novel mechanism was elucidated in the Cr(salen)-catalyzed ARO reaction in which the catalyst was discovered to perform dual roles [9]. The synthesis and characterization of the Cr(salen)N3 complex 2 allowed the identification of this species as the active catalyst in the ARO reaction, suggesting that one role of the Cr catalyst was to deliver the azide nucleophile. X-ray crystallographic and IR spectroscopic analysis of 2 revealed a 6-coordinate geometry with the Lewis acid-... 

The N-(purin-6-yl)pyridinium chloride 309 was more reactive on substitution with a weak azide nucleophile (yield 87%) then the 6-chloro-analogue (yield 25%) at the same reaction conditions (96JCS(P1)15) (Scheme 89 and 90). 

The expected reactions of the cyano group attached to triazine ring carbon with amine, alcohol, and azide nucleophiles have been described <90NKK396>. Reduction of ketone to alcohol with sodium borohydride <88HCA712> and trichloromethyl groups to methyls with lithium aluminum hydride are also reported <86MI 6l2-02>. 

Cyclic sulfite 211 derived from a,/3-dihydroxy hydroxamate 210 underwent stereoselective ring opening at the a position to give azido alcohol 212, which further cyclized to )Q-lactam derivative 213 under Mitsunobu conditions (90TL4317) (Scheme 50). A similar Q-lactam synthesis by the ring opening of cyclic sulfate 214 derived from tartaric acid with azide nucleophile followed by reduction has been reported (90JOC5110) (Scheme 51). 

As with a cyclic sulfite, cyclic sulfamidite 158 also undergoes stereoselective ring opening to furnish azido amine 222, which is a precursor for the synthesis of diamines 223 (95TA1667) (Scheme 55). The azide nucleophile always attacks the carbon having oxygen functionality. 

Chlorobenzene)Mn(CO)3 is easily prepared and undergoes direct substitution with alkoxy, phenoxy, thiolate, amine, and azide nucleophiles as well as aniline and selenide nucleophiles [2]. (Fluorobenzene)Mn(CO)3 is known, but so reactive it is said to solvolyze rapidly during purification [97]. A promising application is the introduction of an asymmetric amine unit that allows differentiation of the two diastereotopic meta positions (in 39) [96]. 

Azide ion (or congener) attack upon nonconjugated alkenes is aided by the use of Dimethyl(methylthio)sulfonium Tetra-fluoroborateP Trans products are obtained and, in general, the amount of anti-Markovnikov product increases with increased azide nucleophilicity, and vice versa. Monosubstituted alkenes favor anti-Markovnikov addition, whereas the opposite occurs with trisubstitution. 1,1-Disubstituted alkenes can give either orientation. 

No silylated compoimds were detected under these reaction conditions, showing that the use of TBAF was two-fold advantageous, for the activation of the azide nucleophile on one hand and the deprotection of iSl-silylated products on the other hand. 

Sodium azide Nucleophilic substitution of ar. nitro groups... 

The experimental evidence obtained for the azide nucleophilic substitution in fluorides 3 and 5 suggests that the reaction follows a different mechanism in each case. a-Glucopyranosyl fluoride 3 yields die substitution product 4 with inversion of the configuration at the anomeric carbon, which is die expected result for a Sn2-type reaction (Scheme 13.5). 

If the relative rate in methanol is taken as 1, then the rates in water, DMSO, DMF, and methyl cyanide (acetonitrile) are 7, 1300, 2800, and 5000, respectively. It is quite clear that the entering azide nucleophile is best solvated in methanol and least solvated in acetonitrile. Thus, the largest amount of energy is required to free azide from methanol in order to form the transition state, and the least energy is needed to remove the acetonitrile solvent. 

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