Oxime reaction with allylboronates

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 reactions of oxime (198) and phenylsulfenimines such as (201) with allyl metal reagents have been described (Scheme 33). The reaction of (198) and allylboronate (144) provides (199) with modest selectivity, while excellent diastereoselectivity was realized in the reactions of (201) and its C-2 epimer with the allylzinc reagent." The corresponding ketone derivatives, however, gave 70 30 mixtures of (204) and (205) upon reaction with diallylzinc, while with allyl Grignard, (205) is almost the exclusive product." The latter result is suggestive of a chelated transition state. 

Treatment of synlanti mixtures of aldoximes (69) with allylboronates generates N-(homoallyl)hydrox-ylamines (70) in good yield (Scheme 6). - The anti oxime reacts faster than the syn isomer. N-(Ho-moallyl)hydroxylamines (70) have been converted to homoallylamines (71) (with iron(II) dihydrolipoate) and have been treated with aldehydes to generate highly functionalized nitrone intermediates (72) for use in 1,3-dipolar addition reactions. 

Reactions of allylboronates with imines [119,120] and oximes [119,121-123] have also been documented. These reactions are attractive because they lead to homoallylic amines as products. They are much slower than similar reactions with aldehydes and the additions are often less selective. Prediction of their stereochemical outcome is complicated by the possibilities that they may proceed via boat-like transition states, and the imine or oxime substrate might undergo E-Z isomerization under the harsh conditions of the additions. Wuts and co-workers, however, observed that (E)-3-tri-alkylsilyl-substituted reagents like 85 are particularly effective for additions to N-ben-zyl imine derivatives (Equation 44) [124]. A few examples of enantioselective additions have been reported [125,126], one of the more successful being the addition of the 2-carboxyester allylboronate 86 to imine 87, yielding exo-methylene y-lactam 88 as a pure enantiomer (Equation 45) [127]. 

The addition of allylboronates 1 to the chiral oxime 2 results in the formation of a hydroxyl-amine. This is a general method for the subsequent reductive generation of primary homoallyl-amines, but with poor diastereoselectivity in the case of 3 and 4. A diastereomeric ratio of 90 10 is achieved in the addition reaction, using the chiral allylboronate 59 (double stcrcodifferenti-ation). 

The stereochemistry of the reactions of oxime ethers and crotylboronates (22) and (23) have been discussed earlier (Scheme 8). The reactions of the corresponding oximes with (22) and (23) appear to follow a similar stereochemical course (Scheme 14). Stereoselectivity, however, is not as high with the isobutyraldehyde and pentanal oximes as it is with phenylaldoxime. The reaction of MeaSi-substituted allylboronate (90) and acetaldehyde oxime performed in refluxing CCU similarly provides a 79 21 mixture of the anti and syn product diastereomers (MeaSi replacing Me in 25 and 26). Excellent stereoselectivity for syn-homoallylamines has been achieved via the Lewis acid catalyzed reactions of aldimines and crotyltributylstannane. ... 

The addition of ( )--y-(trimethylsilyl)allylboronate (93) to racemic oxime (92) has been utilized by Wuts and Jung in connection with a total synthesis of cannabisativine (Scheme 7). Paralleling the investigations of Hoffmann and Endesfelder using ( )-crotylboronate (87 see equation 20), the reaction of (93) is anti selective and affords diastereomeric hydroxylamines (94) and (95). The diastereofacial se-... 

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