Stannanes allylation with

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

Ally 1(trialky 1)- and allyl(triaryl)stannanes react with aldehydes and electron-deficient ketones on heating to give homoallylic alcohols48, although rather high temperatures are required. 2-Methylene-l,3-bis(tributylstannyl)propane is somewhat more reactive49-50, as are allyltin halides, which can be used in the presence of water51. 

The Stille reaction has been successfully applied to a number of macrocyclic ring closures.207 In a synthesis of amphidinolide A, the two major fragments were coupled via a selective Stille reaction, presumably governed by steric factors. After deprotection the ring was closed by coupling the second vinyl stannane group with an allylic acetate.208... 

Allylic silanes and stannanes react with various electrophiles with demetallation. These reactions can occur via several related mechanisms. Both types of reactants can deliver alkylic groups to electrophilic centers such as carbonyl and iminium. 

A. y-Oxygen-Substituleel Stannanes. Oxygenated allylic stannanes have been synthesized and used advantageously in several types of syntheses. Both a- and y-alkoxy and silyloxy stannane can be prepared by several complementary methods.177 C-y-Alkoxy and silyloxy allylic stannanes react with aldehydes to give primarily syn... 

Scheme 10.17 illustrates allylation by reaction of radical intermediates with allyl stannanes. The first entry uses a carbohydrate-derived xanthate as the radical source. The addition in this case is highly stereoselective because the shape of the bicyclic ring system provides a steric bias. In Entry 2, a primary phenylthiocar-bonate ester is used as the radical source. In Entry 3, the allyl group is introduced at a rather congested carbon. The reaction is completely stereoselective, presumably because of steric features of the tricyclic system. In Entry 4, a primary selenide serves as the radical source. Entry 5 involves a tandem alkylation-allylation with triethylboron generating the ethyl radical that initiates the reaction. This reaction was done in the presence of a Lewis acid, but lanthanide salts also give good results. 

A second route to nonracemic /-oxygenated allylic stannanes utilizes an enantioselective deprotonation of allylic carbamates by BuLi in the presence of (—)-sparteine. The configurationally stable a-lithio carbamate intermediate undergoes enantioselective S/,-2 reaction with Bu3SnCl and Mc SnCI (Scheme 28)65. Once formed, the /-carbamoyloxy stannanes can be inverted by successive lithiation with. s-BuLi and stannation with R3SnCl (Scheme 29)65. The former reaction proceeds with S/.-2 retention and the latter by Sf2 inversion. Nonracemic allylic carbamates can also be used to prepare chiral stannanes. Deprotonation with. s-BuLi TMEDA proceeds stereospecifically with retention (Scheme 29)65. 

Radical allylations with allylsilanes 71 occur under mild conditions in good to excellent yields, provided that the radical precursor and the silane have the appropriate electronic pairing [85]. The two examples in Reactions (7.75) and (7.76) show the reactivity matching of the allylating agent with the radical. These reactions offer tin-free alternatives for the transformations that are currently carried out by allyl stannanes. 

Scheme 57 illustrates an example of this process coupling of the lithio reagent derived from vinyl stannane 237 with epoxide 242 leads to the C-disaccharide derivative 243 in good yield. A double transmetallation to give an organocopper reagent 244 can facilitate the C-glycosylation reaction with allyl halides [80] (Scheme 58). 

Allylic stannanes condense with nitro dienes in the presence of titanium tetrachloride to give alkenyl a-chlorooximes treatment of the a-chlorooximes with base then affords bicyclic isoxazolines.50 Thus, cyclization of the intermediates (107a-c), obtained from appropriate 1 -nitro- 1,5-hexadienes and (3-propenyl)trimethyltin, gave bicyclic isoxazolines (Scheme 31). Cyclization occurred exclusively on the double bond with the longer (three-atom vs. two-atom) intervening bridge, even when that double bond was trisubstituted. 

In the presence of Lewis acids allyl silanes and stannanes react with epoxides generally at the sterically less demanding carbon atom. Other electron-rich alkenes, such as ketene acetals, can also be used as nucleophiles. The strong Lewis acids required might, however, also lead to rearrangement of the epoxide before addition of the nucleophile can occur (last reaction, Scheme 4.72). 

Elemental antimony is known to mediate the Barbier-type allylation of aldehydes by allylic halides.35 The active intermediates are believed to be allylic antimony(m) species, which are generated from the antimony(O) and the halides. In fact, allylic dichlorostibanes, produced by metathesis of SbCl3 with the corresponding allylic stannanes, react with benzaldehyde to give homoallyl alcohols, where the C-C bond is constructed with -selectivity (Equation (l)).36 Fluoride salts such as KF, NaF, RbF, and CsF accelerate the Sb-mediated Barbier-type allylation with allyl bromide in aqueous media (Equation (2)).37 In the absence of the fluoride ion, no allylation occurs. Although aromatic and aliphatic aldehydes are allylated in good yields by a combined use of Sb-KF, acetophenone, cyclohexanone, and methyl pyruvate remain untouched. 

Organotin chemistry is useful because the familiar patterns of organosilicon chemistry are followed but the reactions proceed more easily because the bonds to tin are weaker and tin is more electropositive than silicon. Thus vinyl, allyl, and aryl stannanes react with electrophiles in exactly the same manner as their silicon counterparts but at a faster rate. 

The palladium-catalyzed reaction of 1 1 mixture of allyl chloride 11 and allyl stannane 3a with alkylidene malonitriles e.g., 4a resulted into the double-allylated product 95 (Scheme 29) [33]. The mechanism of this reaction is... 

Analogous to the allylation with allylsilanes and -stannanes, the transformations, vinylallylation, propargylation, allenylation, alkenylation, alkynylation, and arylation, are viable by the use of an appropriate reagent in the presence of a titanium Lewis acid these are surveyed in the review articles cited both in the Introduction and in this section. The stereochemistry of the reaction of a (vinylallyl)silane in the presence of TiCU has been reported [234]. Equation (113) shows that the major reaction of this silane and isobutyraldehyde occurred mainly in the anti sense with a ratio of anti to syn attack of 90 10 at the terminus remote from the silyl group. Essentially the same stereochemical outcome was observed for the same reaction with the corresponding trimethylsilyl derivative. The intramolecular reaction with an acetal, however, proceeded less selectively the anti syn ratio was 60 40 (Eq. 114) [234]. 

As in the direct stannane carboxylation the carboxylative coupling is thus far limited to allyl stannanes RSnBu3 with R = PhCH2, Ph, vinyl, PhC=C- all fail to react. The structure of the... 

The relative diastereoselectivity in the indium trichloride-mediated allylation with allylic stannanes in water is for the anti homoallylic alcohol [204]. The reactions are anti selective regardless of the geometry of the starting 2-butenylbro-mide. The in-situ-generated allylic indium species undergoes reaction with the... 

Trimethyl((V-phenylbenzimidoyl)stannane reacts with halides such as benzyl or allyl bromide, benzoyl chloride, or methyl iodide in the presence of KF and 18-crown-6 to give the corresponding ketimine presumably attack of the fluoride ion at tin gives an imidoyl anion equivalent73... 

In addition, recent studies towards the synthesis of bryostatin 1 have described high diastereoselectivity for the chelation-controlled condensation of the substituted stannane 68 with ent-33 leading to the desired i yn-product 69 via 70 (Scheme 5.2.17).While ketones have rarely been explored as reactive electrophiles for stereoselective allylations, proximate coordination of a Lewis acid through a-chelation can produce favorable results, as illustrated in the exclusive formation of the tertiary homoallylic alcohol 72 from 71 (Scheme 5.2.17).28... 

Williams " has reported an enandocontroUed approach by low temperature formation of a six-membered coordination complex of chiral Af-enoyl-l,3-oxazolidin-2-ones with ZrCU- Conjugate Se additions of a variety of substituted allylic stannanes occur with moderate to high stereoselectivity based on the oxazolidinone auxiliary, as shown by the conversion of 176 to 177 (Scheme 5.2.38). The precise role of the chiral auxiliary for determining the facial selectivity in the reaction is not fully understood. 

Scheme 5.2.50 Chiral Imines for dlastereoselectlve allylation with stannane 223...

Matched and mismatched characteristics have been observed in reactions with non-racemic a-benzyloxypropionaldehyde. The matched asymmetric allylation of (E)-stannane 278 with (S)-aldehyde, initiated by complexation with BFs OEta, exclusively provides the E-4.5-syn-5,6-anti compound 279 as the expected Felkin-Anh adduct (Scheme 5.2.61, top). On the other hand, the Q -chelation-controlled process can also be achieved via a matched case of double diastereoselection using the (S)-stannane 280 and pre-complexation with MgBr2 OEt2. The syn product 281 is rationalized via the antiperiplanar transition state 282 (Scheme 5.2.61, bottom). 

Elemental antimony [20] and SbCls-M (M = Fe, Al) binary systems [21] mediate the Barbier-type allylation of aldehydes by allylic halides or phosphates to afford homoallyl alcohols (Scheme 14.1). In the presence of fluoride salts a similar allylation with allyl bromide proceeds in H2O [22]. Allylic dichlorostibanes, generated from allylic stannanes and SbCls, react with benzaldehyde to give homoallyl alcohols (Scheme 14.2) [23]. 

Chiral titanium complexes 4 and 5, which were developed as chiral catalysts for asymmetric carbonyl-ene reactions with prochiral glyoxylate esters [50], were first apphed to the catalytic asymmetric allylation of carbonyl compounds by Mikami and Nakai (Scheme 5) [9]. The titanium catalysts are prepared from (S)-binaphthol and diisopropoxytitanium dihahde (X=C1 and Br) in the presence of 4 A molecular sieves. Using these catalysts, glyoxylates are enantio- and diastereoselectively allylated with allylic trimethylsilanes or allylic tributylstan-nanes. High levels of enantioselectivity and syn selectivity are observed for (E)-crotylsilane and -stannane. The syn selective allylation reaction is believed to proceed mainly through an antiperiplanar transition state. 

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