0-Allyl hydroxylamines

The secondary allylic methylamine 324 can be prepared by the allylation of A -methylhydroxylamine (323), followed by hydrogenolysis[201], Monoallylation of hydroxylamine, which leads to primary allylamines, is achieved using the jV,0-bis-Boc-protected hydroxylatnine 326. N -... 

Hydroxylysine (328) was synthesized by chemoselective reaction of (Z)-4-acet-oxy-2-butenyl methyl carbonate (325) with two different nucleophiles first with At,(9-Boc-protected hydroxylamine (326) under neutral conditions and then with methyl (diphenylmethyleneamino)acetate (327) in the presence of BSA[202]. The primary allylic amine 331 is prepared by the highly selective monoallylation of 4,4 -dimethoxybenzhydrylamine (329). Deprotection of the allylated secondary amine 330 with 80% formic acid affords the primary ally-lamine 331. The reaction was applied to the total synthesis of gabaculine 332(203]. 

Allyl or benzyl groups on the nitrogen facilitate the process. The rearrangement appears to be intramolecular (13), proceeding by a cycHc mechanism as in the case of /V-2-buteny1-/V-metby1 aniline oxide giving /V-methyl-0-1-methylallyl-/V-phenyl-hydroxylamine. 

Furthermore the formation of <9-substituted hydroxylamines 12, e.g. by migration of an allyl or benzyl substituent, is possible ... 

Allylation of acyloyl-imidazoles and pyrazoles61 with allyl halide mediated by indium in aqueous media provides a facile regioselective synthesis of P, y-unsaturated ketones (Scheme 11.1), which has been applied to the synthesis of the monoterpene artemesia ketone. The same product can be obtained by indium-mediated allylation of acyl cyanide (Eq. 11.35).62 Samarium, gallium, and bismuth can be used as a mediator for the allylation of nitrones and hydrazones to give homoallylic hydroxylamine and hydrazides in aqueous media in the presence of Bu4NBr (Scheme 11.2).63 The reaction with gallium and bismuth can be increased dramatically under microwave activation. 

Reactions of Allylation and Propargylation Allylation of prochiral and chiral nitrones (292) with allylmagnesium chloride leads to homoallylic hydroxylamines (416), which via an iodo cyclization step are converted to 5-(iodomethyl)isoxazolidines (417) (Scheme 2.186) (202, 213, 666-668). 

Addition of allylic zinc bromides to nitrones, generated in situ from allylbro-mides and zinc powder in THF (670), allyltributylstannane (671) and lithiated allyl ferf-butyldimethylsilyl ether (672), proceeds regioselectively in good yields and is used to synthesize homoallyl hydroxylamines (Scheme 2.189). The latter were subjected to an iodo cyclization reaction (see Scheme 2.186). 

The use of allylindium reagent, generated in situ, makes it possible to introduce the allyl group into C-aromatic aldonitrones, in dimethylformamide DMF-H2O at room temperature (675). Under similar conditions the indium-catalyzed reaction of propargyl bromide with nitrones leads to the corresponding homoalkynyl hydroxylamines (Scheme 2.191) (676). 

Namely, allyl alcohol is successively treated with diethylzinc, (R,R) dipropyl tartrate, and 4-methoxybenzohydroximinoyl chloride (163) to afford the enantiomeric isoxazoline alcohol 166, which under the Jones oxidation conditions affords the corresponding carboxylic acid derivative (167). Treatment of compound 167 with hydroxylamine-O-triflate followed by tri-fluoroacetic acid gives rise to the desired enantiomeric 165 in high excess enantiomeric yield. The synthesis of other isosteric analogues of 165 was reported in the same paper. None of the isosteric analogues exhibits LpxC inhibitory and antibacterial activities [103]. 

HydroxylaminationIn the presence of this Pd(0) catalyst, allyl esters react with hydroxylamines to provide N-allylhydroxylamines, which are reduced by zinc in dilute HC1 to secondary allylamines. 

Treatment of hydroxylamines 4 (R1 = cyclohexyl, Ph or 3,4-(MeO)2CgH3) with acetone gives nitrones 5, which are transformed by Grignard reagents R2MgBr (R2 = Me, Et, Bu, Ph or allyl) into the hydroxylamines 6 the latter are converted into the hindered secondary amines 7 by means of carbon disulphide10. 

Reaction 38 shows that hydroxylamines can cause amination at allylic positions. Fe(II) phthalocyanine (222c) was the most effective catalyst. Other catalysts and substrates were also investigated623. Complexes of Mo(VI) were less effective than 222c as catalysts for amination processes of this type624. 

Hydroxylamine derivatives are ambident nucleophiles. For example, N-benzylhy-droxylamine functions as an N-nucleophile in the Ir-catalyzed allylic substitution, while N-Boc-hydroxylamine yields mixtures of the N- and O-substituted products in Ir- as well as Pd-catalyzed allylic substitutions. Accordingly, either O- or N,0-protected hydroxylamine derivatives need to be used as nucleophiles [63]. 

In our hands, base-activated phosphoramidite-Ir complexes were not suited for the allylation of hydroxylamine and hydrazine derivatives (R. Weihofen and G. Helmchen, unpublished results). However, interesting results were obtained by Takemoto and coworkers with Pybox type ligands (Scheme 9.30) [40]. Phosphates... 

Scheme 9.30 Allylic substitutions with a hydroxylamine derivative as nucleophile.

Sigmatropic rearrangement of allylic tertiary amine-A -oxides to give O-allyl hydroxylamines ... 

Allylboronates of type 103 react with equivalent amounts of aldoximes 102 (equation 73) giving allylhydroxylamines 104 in good yields. Similar reactions of aldoximes and glyoxylate oxime ethers with allyl bromide and indium also provide hydroxylamines. Additions of substituted allyl boronates to oximes produce mixtures of stereoisomers with ratio highly dependent on the steric size of substituents in both molecules. Addition of allyltri-n-butyltin to aldoxime ether 105 (equation 74) was found to proceed with a considerable diastereoselectivity. 

Diastereoselective [2,3]-sigmatropic rearrangement of lithium O-allyl-A-benzylhy-droxylamides (195) bearing a stereogenic center adjacent to the migration terminus was reported 3" 3 (equation 57). When the (E) and (Z)-iV-benzyl-0-(4-methoxy-4-phenylbut-2-enyl)hydroxylamines (194) rearrange, a chelation by the lithium ion occurs and the (Z)-(lR5, 2R5 )-l-phenyl-l-methoxy-3-iV-benzylaminobut-3-ene (196) is the major product... 

An interesting transformation of a conformationally restrained allyl amide 232 to an ot-hydroxy-cyclopentenyl hydroxylamine 236 has been reported. The mechanism is thought to involve a series of reversible reactions leading ultimately to 234, which fragments irreversibly to 235. Hydrolysis of the ester accounts for the observed product 236 (Scheme 8.64). 

The requisite hydroxylamine function for such cyclizations can also be generated from a precursor having a nitro group. This novel route has provided access to hitherto unknown l-hydroxy-6-allyl-, and -6,6-bisallyl-piperazine-2,5-diones (91UP1). The starting material is an W-nitroacetyl amino acid ester that can be either mono-or bis-allylated at the methylene adjacent to the nitro group. Reduction of the N02 to NHOH using zinc/ ammonium chloride, followed by cyclization, leads to the desired products (Scheme 76). Compound (215) is unique in that it possesses a chiral center at C-3 and a quaternary carbon at C-6 on a l-hydroxypiperazine-2,5-dione system. 

Chiral oxime ethers 229 of R)- and (5 )-0-(l-phenylbutyl)-hydroxylamine (ROPHy/ SOPHy) react with Grignard reagents in the presence of BFs OEta in toluene at —78°C yielding addition products with high diastereoselectivities (equation 154) . The resulting chiral hydroxylamine derivatives have been converted enantioselectively to primary amines, or (when R = allyl) to / -amino acids. 

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