Allylation of aldimines

Allyltantalum-mediated allylation of aldimines was reported by Bhuyan et al. in 1993 these workers compared tantalum and bismuth organometallic reagents over a series of transformations. Up to 60% yield was obtained for tantalum-mediated allylation (benzylidene aniline as electrophile). Bismuth reagents offered better yields in the cases compared but, in all cases, a remarkable effect for the addition of Bu NBr was observed.186... 

The bismuth- or tantalum-promoted allylation of aldimines 187 (R1 = Ph or PhCH=CHCH2 R2 = Me, Ph or PhCH2) with allyl bromide in the systems Bi/Bu4N+ Br /MeCN or Ta/Bu4N+ Br /MeCN yields the amines 188193. 

Imidazoles/benzimidazoles and chiral carbinamines are of particular importance [73, 74], Recently, Leighton et al. developed a method for enantioselec-tive imidazole directed allylation of aldimines and ketimines [75] with an analogue of 31. 

Phenols have been employed as directing groups in the enantioselective allylation of aldimines and ketimines using allylchlorosilane reagents.45... 

Allylation of aldimines and sulfonimines with indium powder in poly(propylene) glycol (MW 1000), a benign and recyclable reaction medium, results in the formation of the corresponding homoallylic amines and sulfonamides in high yields (Equation (62)).265... 

Combined use of BF3-OEt2 and AcOH was found to be effective for allylation of aldimines. The catalyst system is also effective for the three-component synthesis of homoallylic amines starting from aldehyde, amine, and allylgermane (Scheme 11.11) [24]. 

The enantioselective allylation of aldimines 8 with the tetraallylsilane-TBAF-MeOH system with use of the chiral bis-7i-allylpalladium catalyst 20a under catalytic, non-Lewis acidic, essentially neutral, and very mild reaction conditions has been achieved (Eq. 11) [9]. The reaction of imines 8 with 1.2 equivalents of tetraallylsilane 25d in the presence of 5 mol% of the chiral bis-Ti-allylpalladium catalyst 20a, 25 mol% of TBAF, and 1 equivalent of methanol in THF-hexane (1 2) cosolvent furnished the corresponding homoallylamines 9 in high yields and good to excellent enantioselectivities. 

Allylation of aldimines 21.86 (Scheme 21.11) derived from o-aminophenol with 21.5a in DMF at 0 °C have also been reported. In an enantioselective variant of this reaction chiral formamide 21.88 (1 equivalent) afforded homoallylic amine 21.87 with modest enantioselectivity (<57% ee). ... 

Compared with aldehyde, the corresponding aldimine is less reactive toward nucleophilic addition however, aldimine is able to coordinate to transition metals more strongly. This latter property of aldimine may be more important than the former in the present reaction, and the allylation of aldimine proceeds much easier than the aUylation of aldehyde. In order to achieve the Lewis acid promoted allylation of aldehydes and aldimines with allylstannane, an excess amount of Lewis acid (>2 equiv) is required. Under such conditions, both aldehyde and aldimine may be equally activated toward allylation, and the allylation of aldehyde takes place selectively. 

Asymmetric allylation of aldimine providing chiral homoallylamines is accomplished by using 5 mol % of 7r-allylpalladium chloride dimer derived from (75)-/3-(-)pinene (Scheme 29)P The pinene moiety serves not only as a chiral auxiliary but also as a dummy 7r-allyl group of unsymmetrical bis-7r-allylpalladium intermediate. The asym-metric induction is successful for aldimines derived from alkylamines (benzy-lamine, p-methoxybenzylamine, and isopropylamine) however, no asymmetric induction is observed for aldimines of aniline. 

Activation by TMSCl has also been applied to the allylstannane allylation of aldimines ", the copper-catalysed conjugate addition of organoaluminium reagents to enones, and in the uncatalysed conjugate addition of organozincs in THF/iV-methylp3Trofidone. Its involvement in the conjugate addition of stabilized... 

A fluoride-triggered autocatalytic process (Scheme 16) has been proposed to account for the formation of homoallylamines (115) on reaction of allyltrimethylsilane (113) with aldimines (114) in the presence of TBAF this represents the first non-Lewis acid-mediated allylation of aldimines by allylsilane. ... 

Efficient methods for stereoselective allylations of aldimines are scarce [19, 22, 39, 44] in comparison with the various methods that have been developed for the corresponding allylations of aldehydes (Chapter 5). One of the early examples was reported by Yamamoto, with aldimine 9 and allyl-9-BBN 10 (Scheme 11.1) [45]. The addition of 9 and 10 furnishes 12 as the sole isolated product. To account for the sense of induction, Yamamoto suggested 11 as the energetically favored transition state structure. In this arrangement, the placement of the methine proton over the ensuing cyclic ensemble effectively minimizes non-bonding steric interactions in comparison with the disfavored transition state structure 13. 

The synthesis of vinylaziridines through reactions between allylic carbenoid reagents and imines (i.e., Darzen-type reactions) was first reported by Mauze in 1980 [13]. Treatment of aldimines or ketimines 16 with gem-chloro(methyl)allyllithium (17) afforded N-substituted vinylaziridines 18 (Scheme 2.6). Similarly, 2,3-trans-N-diphenylphosphinyl-2-vinylaziridines 21 were prepared with good stereoselectivities (trans cis= 10 1 Scheme 2.7) by treatment of a-bromoallyllithium (20) with N-diphenylphosphinyl aldimines 19 in the presence of zinc chloride [14]. 

Homoallylic amines result from the reaction of aldimines, previously activated by boron trifluoride etherate, with allylic bromides in the presence of chromium(II) chloride, e.g. equation 68194. 

Scheme 6.40 Product range of the 11-catalyzed asymmetric Strecker reaction of aromatic and aliphatic N-allyl-protected aldimines.

Bismuth(lll) chloride catalyzes the intramolecular hetero-Diels-Alder reaction of aldimines, generated in situ from aromatic amines and the A -allyl derivative of o-aminobenzaldehyde, in acetonitrile at reflux to generate [l,6]naphthyridine derivatives <2002TL1573>. The hetero-Diels-Alder reaction of 3-aryl-2-benzoyl-2-propeneni-triles and enol ethers yields 2-alkoxy, 6-diaryl-3,4-dihydro-2//-pyran-5-carbonitriles (Scheme 29) <1997M1157>. 

In the presence of a Lewis acid or fluoride ion, imines react with allylsilane to yield the homoallylic amines with high stereoselectivity119,120. Thus, treatment of N-galactosylaldimine 81 with allylsilane in the presence of excess of SnCU yields the corresponding allylated product 82 (equation 54). It is noted that aliphatic aldimines do not react under these conditions. Fluoride ion promoted crotylation of aldimines proceeds in a regiospecific and diasteroselective manner121. A pentacoordinate silicate moiety is involved in this reaction. 

A C2-chiral bisformamide (18) derived from diaminocyclohexane catalyses the enantioselective allylation of simple aldimines, using allyltrichlorosilane in the presence of L-proline.44 The more immediate allylating agent is, in fact, L-proline derivative (19), formed in situ, and observed by NMR and MS. 

The allylation of hydrazones derived from arylalkyl ketones [42] and of N-aryl aldimines in DMF at 0 °C [46] have also been reported. 

During the reaction of the doubly activated allyl halides with primary and secondary amines no 2-amino-substituted cyclopropane derivatives could be isolated, but instead ring-opened products are formed. Primary amines give rise to the formation of aldimines (332) while secondary amines afford formally substitution products (333) . The formation of these products can be explained by ring cleavage of non-isolable electrophilic 2-aminocyclopropanes (331) as outlined in equation 104. 

Models used to explain and predict diastereofacial selectivity in related carbonyl addition reactions (Figure 7) can be utilized to predict similar selectivity in allyl organometallic-aldimine condensations. As a consequence of the type of imine substitution, addition reactions can be divided into two types (i)... 

The addition of organolithiums u thylethylamine forms mainly one dia lion, therefrom chiral amines are avail a-Sulfinyl carbanions also add sopinocampheylborane is an allyl i whereas high-leveled 1,6-asymmetnc 4,5-dicyclohexyl-2-vinyl-1,3-dioxolar Strecker reaction to establish a n capable of creating either a tertiary The peptido-imine 60 proves to be an of aldimines. -" On catalysis of the V-benzhydrylaldimines affords a-amn... 

Allylation. Allyl halides are converted to allyltitanium compounds by r-PrMgBr/jr-PrOj Ti, which can be used for allylation of carbonyl compounds and aldimines. With imines derived from a chiral a-phenethylamine, the reaction is highly diastereoselective following the Cram pattern exhibiting a 1,3-asymmetric induction. 

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