Subject allylic azides

The research team of J. Tadanier prepared a series of C8-modified 3-deoxy-P-D-manno-2-octulosonic acid analogues as potential inhibitors of CMP-Kdo synthetase. One of the derivatives was prepared from a functionalized olefinic carbohydrate substrate by means of the Wohl-Ziegler bromination. The stereochemistry of the double bond was (Z), however, under the reaction conditions a cis-trans isomerization took place in addition to the bromination at the allylic position (no yield was reported for this step). It is worth noting that the authors did not use a radical initiator for this transformation, the reaction mixture was simply irradiated with a 150W flood lamp. Subsequently the allylic bromide was converted to an allylic azide, which was then subjected to the Staudinger reaction to obtain the corresponding allylic amine. 

Schkeryantz and Pearson (59) reported a total synthesis of ( )-crinane (298) using an intramolecular azide-alkene cycloaddition (Scheme 9.59). The allylic acetate 294 was first subjected to an Ireland-Claisen rearrangement followed by reduction to give alcohol 295, which was then converted into the azide 296 using Mitsunobu conditions. Intramolecular cycloaddition of the azide 296 in refluxing toluene followed by extrusion of nitrogen gave the imine 297 in quantitative yield. On reduction with sodium cyanoborohydride and subsequent reaction with... 

In analyzing their data, Sneen and Larsen had to correct for salt effects, since they were comparing rate with azide present to rate without.107 Schleyer and co-workers have criticized Sneen s conclusions by pointing out the uncertainties involved in such corrections,108 and Sneen has replied, justifying his earlier conclusions and presenting similar evidence for a-phenylethyl systems,109 and for an allylic system.110 The question is far from settled, and will continue to be a subject of investigation.111... 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

An efficient stereoselective synthesis of (-l-)-241D (13) using reductivea-mination was reported by Rao and coworkers [22]. Decanal (70) was subjected to an enantioselective Maruoka allylation using titanium complex of (S,S)-BINOL and furnished 71 with 98% ee. Tosylation of the hydroxyl group of 71 followed by azidation gave 72. The azide 72 was reduced to amine followed by protection with CbzCl to give 73. Sharpless AD of 73 with AD mix... 

Conjugated ester 6.271 was treated with diisobutylaluminum hydride to reduce the ester moiety to an alcohol. This allylic alcohol was subjected to Sharpless asymmetric epoxidation. 1 Opening the epoxide (5.272) with azide was followed by protection of the diol moiety to give 5.273.154 Reduction of the azide, protection of the amine, and oxidation gave lactam 5.274.154 Acid hydrolysis gave 4-amino-2,3-dihydroxy-3-methylbutanoic acid, 6.275, a degradation product of carzinophilin.i55[Pg.231]

Starting materials, like 141, which are accessible from alkenes by azido-selenenylation, afforded only in a few cases vinyl azides exclusively as shown by the example 141 142 (Scheme 5.19). In most cases, after oxidation of the vicinal phenylseleno azides and elimination reaction on the intermediate selenoxide, mixtures of allyl and vinyl azides were obtained. Ring opening of trialkylsilyl-substituted epoxides was utilized several times for stereoselective synthesis of vinyl azides. Thus, treatment of the frani -contigured oxiranes 143 with azidotrimethylsilane and boron trifluoride etherate yielded cis-conflgured products 145. This result was explained by the intermediate 144 which should undergo anti-elimination. On the other hand, when subjected to sodium azide in dimethylformamide, epoxides 146 were transformed into vinyl azides 148 via... 

It is tempting to think that allylic cations would behave similarly to other stabilized cations in their reactions with alkyl azides. " In practice what happens is invariably an initial formal [3+3] cycloaddition of azide to the allylic cation, which is followed by a migration event (typically of hydride) or trapping by a nucleophile. Pearson and coworkers found that when sulfonylindole 27 was treated with SnCk at -78 °C, followed by basic workup, triazoline adducts 28 were obtained as mixture of chloride epimers (Scheme 7.24). When A -alkyl indoles (e.g. 29) were subjected to Lewis acidic conditions, tri-azines such as 30 were obtained as the sole products. In the former case involving an iV-sulfonyl indole, a [3+2] cycloaddition pathway explains the product, whereas the iV-alkyl indoles examined underwent [3+3] cycloaddition. 

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