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Allylations with Allylstannanes

Allylalwn. This compound is a useful Lewis acid for activation of electrophiles containing oxygen to allylation with allylstannanes. It is usually more effective than BF3 etherate. ... [Pg.28]

Table 10. Titanium-mediated allylation with allylstannanes. Table 10. Titanium-mediated allylation with allylstannanes.
The similar Zr and substituted BINOL catalyst system can also be used for asymmetric Mannich-type reaction, Strecker reaction, hetero Diels-Alder reaction, allylation with allylstannanes, as described in the following text. [Pg.301]

In an elegant demonstration of the versatility of Corey s chemzymes, Williams used the oxazaborolidine bromoborane 44 in an allylation with allylstannane 43, en route to a critical segment of phorboxazole (Scheme... [Pg.162]

The a-bromo-7-lactone 901 undergoes smooth coupling with the acetonyltin reagent 902 to afford the o-acetonyl-7-butyrolactone 903[763j. The o-chloro ether 904, which has no possibility of //-elimination after oxidative addition, reacts with vinylstannane to give the allyl ether 905, The o -bromo ether 906 is also used for the intramolecular alkyne insertion and transmetallation with allylstannane to give 907[764],... [Pg.261]

The indium-mediated allylation carried out with allylstannanes in combination with indium chloride in aqueous medium was reported by Marshall et al.113 Allylindium was proposed as the reaction intermediate. Various aldehydes can be alkylated very efficiently with 3-bromo-2-chloro-l-propene mediated by indium in water at room temperature. Subsequent treatment of the compound with ozone in methanol followed by workup with sodium sulfite provided the desired hydroxyl ester in high yield.114... [Pg.237]

The radical source must have some functional group X that can be abstracted by trialkylstannyl radicals. In addition to halides, both thiono esters and selenides are reactive. Allyl tris(trimethylsilyl)silane can also react similarly.232 Scheme 10.11 illustrates allylation by reaction of radical intermediates with allylstannanes. [Pg.660]

Alkyl halides possessing / -hydrogens are usually poor substrates for carbonylative cross-coupling due to competitive / -hydride elimination/ Allyl chlorides can be used in carbonylative cross-coupling with allylstannanes/ phenyl-, 3-furyl, or vinylstannanes " to afford allylketones in modest to good yields. Divinylketones can be accessed through the reaction of vinylstannanes with vinyl iodides or vinyl triflates, with the latter requiring the addition of LiCl. Synthetic potential of this method has been proved in the formation of macrocyclic ketone jatrophone. In the reaction of vinyl triflates with tetramethyltin or aryltrimethylstannanes the additional activation by ZnCle is required. [Pg.413]

Allylation of Pyranosyl Compounds with Allylstannane [19,20]. A solution of the methyl-(p-D-galactopyranosyl chloride) onate 22 (953.5 mg, 1.8 mmol) in 30 mL of dry, oxygen-free THF, was heated to 60°C. To this solution under nitrogen, were added the tributylallyl tin 23 (5.2 mL, 14.7 mmol) and A1BN (15 mg, 0.1 mmol). After 20 h, the solvent was evaporated, and the residue was taken up in 5 mL of acetonitrile. The acetonitrile layer was extracted with 20 mL of n-hexane and then concentrated. Chromatography on silica gel (toluene-acetone, 4 1) afforded the product 24 (889 mg, 93%), containing two anomers. Nuclear magnetic resonance (NMR) spectroscopy showed a ratio of the two anomers of 1.8 1. [Pg.520]

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... [Pg.344]

As organotin compounds (organostannanes) undergo smooth Pd-catalysed transmetallation, aryl halides react with a wide variety of aryl-, alkenyl- and alkylstannanes [139]. Coupling with allylstannane is the first example [140]. The reaction is called the Migita-Kosugi-Stille or Stille coupling. Aryl, alkenyl, allyl, alkynyl and benzyl... [Pg.68]

The reactions of a-(arylsulfonyl)acetophenones with allylstannane in the presence of AIBN give a nearly 1 1 mixture of allyl tosyl sulfone and the corresponding ketone. NMR studies reveal the generation of tin enolate during the reaction course (Equation (S3)).238... [Pg.365]

The chiral titanium complex BINOL-T1CI2 also catalyzes the asymmetric carbonyl addition reaction of allylic silanes and stannanes. Thus the addition reaction of glyoxylate with (E)-2-butenylsilane and -stannane proceeds smoothly to give the syn product in high enantiomeric excess (eq 12). The syn product thus obtained can be readily converted to the lactone portion of verrucaline A. The reaction of aliphatic and aromatic aldehydes with allylstannane is also catalyzed by BINOL-TiC to give... [Pg.93]

Umani-Ronchi et al. [56] investigated the asymmetric allylation of aldehydes with allylstannane in the presence of chiral bis(oxazoline) ligands and several metal salts (Sch. 31). Combination of zinc halides and the bis(oxazoline) ligand 70 gave the ally-lated product 71 with moderate enantioselectivity (40 % ee), while other metal salts afforded either no product or racemic products. Because the formation of an allyl-zinc-bis(oxazoline) species was excluded on the basis of the NMR experiments, the reaction was considered to proceed by a Lewis acid-mediated pathway. [Pg.81]

A new synthetic design, based on a titanium Lewis acid consisting of two titanium centers in the same molecule, such as A in Fig. 9, has been reported. This titanium species is more active in allylation with an allylstannane than species B which has only one titanium center per molecule and is a conventional Lewis acid (Eq. 107) [281]. The intermediate C, in which double coordination of the oxygen functionality to both titanium atoms has been proposed, would account for the efficiency of the species A in this reaction. [Pg.697]

Although allylation of imines with allylsilanes is encountered less frequently, that with allylstannanes seems more common, probably because of the enhanced nucleo-philicity of the tin reagent compared with the silyl counterpart. Equations (109) [292] and (110) [293,294] illustrate the allylation of imines. In the former reaction, a catalytic amount of the L wis acid, TiCl(OTf)3, is sufficient to bring the reaction to completion. Intramolecular allylation of imines [295] or hydrazones [296] led to the stereoselective construction of amino-cyclic structures, as shown in Eq. (HI) [296]. [Pg.700]

Alkylations. The effect of subjoined Lewis acid (e.g., trimethyl borate) on the catalytic ally lation of aldehydes with allylstannanes promoted by a BINOL-Ti complex has been examined. With allenyltributylstannane the products are homopropargyl alcohols.. Allylation in a Sn(II)-mediated Barbier reaction exhibits much lower ee, although jllenylation with (terminally substituted) propargyltributylstannanes shows good results. 4-Trimethylsilylbut-2-ynyl)tributylstannane undergoes destannylative addition to... [Pg.25]

Allylations, Reaction of a-bromoketones with allylstannanes in the presence of SnCl2 leads to allyl ketones. The new skeletons arise from an in situ rearrangement process (from the bromohydrin derivatives). y-Selective allylation is mediated by the SnClj-CuCl2 system in water-dichloromethane. ... [Pg.373]

Addition to C=0. Hydrates of a-ketoaldehydes react selectively at the aldehyde group with allylsilanes under the influence of YbfOTfjj at room temperature. The allylation of aldehydes with allylstannanes is accelerated by benzoic acid." Another method for the synthesis of homoallylic alcohols is by the ene reaction, thus y,6-unsaturated a-hydroxy esters are obtained from glyoxylic esters at room temperature in a catalyzed process. ... [Pg.431]

There are very few examples of Lewis base-promoted allylations of aldehydes with allylstannanes. In 1992 Baba disclosed an intriguing method for allylation of aldehydes with allyl- and 2-butenyltributylstannanes in the presence of catalytic-amounts of dibutyltin dichloride and certain coactivators such as tetrabutylammo-nium iodide, tributylphosphine oxide, HMPA or tetraphenylphosphonium iodide [76]. No definitive mechanistic information is available on the role of the co-activators the authors speculate that the ligands accelerate the metathesis to form allyldibutyltin chloride which is the actual nucleophile. The same group has recently reported the use of a lead(II) iodide/HMPA catalyst for the allylation of a,yff-epoxyketones [76bj. [Pg.334]

Diastereoselective radical allylations have been studied in many different contexts, and a plethora of information exists regarding stereocontrol in these reactions. Allylations have been performed using the traditional trapping and )9-elimination sequence occurring typically with allylstannanes as well as a stepwise atom transfer/ elimination sequence found to occur with allylsilanes. Stereochemistry is commonly controlled through the use of chiral auxiliaries or by 1,2-induction, and functionalized anh -aldol and amino acid products are available using this established methodology. [Pg.514]

Highly diastereoselective allylations were also achieved in a slightly different manner through radical addition to chiral oxazolidinone acrylate and trapping with allylstannane [25]. In reactions with a,yS-unsaturated substrates, the Lewis acid... [Pg.515]

Pyridines, quinolines,50 isoquinolines,51 and imidazoles52 react with allylstannanes in the presence of acyl halides, via the corresponding (V-acyl salts, to give the l-acyl-2-allyl derivatives of the 1,2-dihydro compounds. [Pg.138]

In the Lewis acid-promoted allylation with allylsilanes, the promoter is usually regarded as activating electrophiles. Thomas [374] and Dias [375] have, however, described SnCLj-promoted allylation reactions proceeding via a transmetalation mechanism (Scheme 10.130). In the latter equation of Scheme 10.130, the formation of the allylstannane species has been observed by NMR spectroscopy [375 b]. [Pg.497]


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Allylation aldehydes with allylstannane catalyzed

Allylstannane

Allylstannanes

With Allylstannane

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