Allylic derivatives allylamines

Recent results indicate that Zr-catalyzed enantioselective ethylmctallation of allyl derivatives not accompanied by -elimination is feasible witb various allylamines, allyl sulfides, and even with allyl alcohol [29,36] (Table 4.5). Although both chemical yields and enantioselectivity are still generally modest, the following favorable examples appear to indicate that further improvements may be expected. In some cases (NMTHI)ZrCpCl2 (9) of C( symmetry and smaller overall steric requirements provide distinct advantages over sterically more demanding C2-symmetric complexes, such as 1, 3, and 8. 

It is well known that silylation of allyl derivatives with vinylsilane catalyzed by a ruthenium hydride complex is accompanied by isomerization ofpropen-l-yl to propen-2-yl derivatives as well as homo-coupling of vinylsilane when equimolar amounts of the initial substances are used. If catalyst I was used in the SC of allyl amide and allyl amine with vinylsilanes, a S-fold excess of olefin to vinylsilane was used to stop homocoupling of vinylsilane, but simultaneously no more than 5% of isomerization of allyl compound was observed [19, 26]. When allyl boronate is used instead of allylamine under mild conditions (20 - 40 °C), the two reactions catalyzed by I and IV yield stereoselectively -product (see Scheme 4) [26]. 

Prior chapters have covered the use of transition metals in asymmetric hydrogenations ( 6.2 and 7.1), hydroborations ( 7.3), hydrosilylations and hydro-cyanations ( 6.3, 6.4, 7.4 and 7.5), cyclopropanations ( 7.19), aldol reactions ( 6.11), allylations of carbanions ( 5.3.2), and some sigmatropic rearrangements ( 10.3). This chapter covers other reactions catalyzed by transition metal complexes including coupling of organometallic reagents with vinyl, aryl or allyl derivatives, Heck reactions allylamine isomerizations, some allylation reactions, car-bene insertions into C-H bonds and Pauson-Khand reactions. 

Deprotection of A-allyloxycarbonylamines can sometimes lead to the formation of small amounts of 7V-allylamines, as the liberated amine can compete with NHEt2 for the jt-allylpalladium complex. However, the increase of diethylamine concentration and larger amounts of palladium catalyst help to eliminate this problem [70]. Another useful method of deprotection applied to 0-allyl derivatives of carbohydrates and natural polyols... 

The furfuryl derivatives 195, with an allyl ether (X = O) or allylamine (X = NMe) type chain linked to a methylenecyclopropane moiety, readily... 

The cyclization of carbamate derivatives of unsaturated amines has proven synthetically useful. Cyclizations of carbamates of allylamines containing a terminal vinyl group give oxazolidinone products (equation 60 and Table 17, entries 1 and 2).99,161 Bromocyclizations of systems with a di- or tri-sub-stituted alkene often give mixtures of oxazolidinones and tetrahydrooxazinones,163 while cyclization of an A -cinnamyl carbamate with phenylsulfenyl chloride gave only the oxazolidinone product.163b,163c The stereochemistry of the cyclization of primary carbamates of either allylic or homoallylic amines is low... 

Cyclizations of urea derivatives of allylamines with selenium reagents have been examined recently (equation 62 and Table 18).98 Cyclization of the allylic ureas produces franj-2-oxazoline derivatives with high stereoselectivity when the double bond is internal (Table 18, entry 2). Although O-methylisourea derivatives can be cyclized to dihydroimidazoles [see Section 1.9.3.2.2(ii)], cyclization with phenylsel-enenyl trifluoromethanesulfonate and trifluoromethanesulfonic acid produces 5,6-dihydro-1,3-oxazines (6-endo products), even when the double bond is monosubstituted (entry 3). 

Structural studies on the mechanism of the THF-catalyzed vinylic lithiation of allylamine derivatives have been performed using 2D and diffusion-ordered NMR spectroscopy.10 NMR evidence has suggested that in THF the mixed aggregate has close contact between the alkene and the /S-CfG of n-BuLi, whereas in the absence of THF, the allyl chain appears to be pointed away from the nearest n-BuLi residues. 

Reactions of glycosyl imines derived from aliphatic aldehydes must be carried out at low temperature due to their higher sensibility towards anomerization. Yields and diastereoselectivity rank in the same region as those achieved for galactosyl homo-allylamines. The results of different stereoselective allylations, are summarized in Table 4.1. 

A preparative method for allylamines is based on the Pd-catalyzed substitution reaction of /V-allylbenzotriazoles by amines. Formic acid is a convenient hydride source for allylic deoxygenation of Baylis-Hillman adducts via their derived acetates, thus the reaction is the conclusion of a three-step process for access to trisubstituted alkenes which contain one electron-deficient group. 

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