Allyltin, with

TABLE 1. Pd-Calalyzed Reaction of Allyltins with Allyl Electrophiles... 

TABLE 2. Pd-Catalyzed Reaction of allyltins with Allyl Halides in the Presence of Maleic Anhydride ... 

Benzyl- and allyltins present a much lower reactivity in Stille coupling than orga-notins containing a Sn-Csp bond. Allyltins have not been frequently used, due in part to the tendency of products to reconjugate after the cross-coupling when ole-finic or aromatic substrates are used as electrophilic partners [38], and the frequent loss of regioselectivity observed whith y-substituted allyltins [39]. A nice application is represented by the reaction of a /3,y-disubstituted allyltin with a naphthoquinone-bromide used in a biomimetic-type synthesis of benzo [a]naphthacene quinines related to Pradimicinone [40] (Scheme 6). 

There is one report of a chiral reagent based on allylaluminum chemistry1 2 3 4 5 10. Bis(2-methyl-propyl)-2-propenylaluminum is treated with tin(II) triflate and chiral diamine ligand 4 to give a reagent, presumably a chiral allyltin species, that reacts with aldehydes at — 78 "C. Good enantioselectivity (80 -84% ee) is obtained with aromatic aldehydes, but with aliphatic aldehydes the selectivity is somewhat lower (53-64%)10. 

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. 

An intermediate allyltin trichloride, possibly stabilized by an oxygen-tin hypervalent interaction, which then reacts with the aldehyde via a chair-like six-membered ring transition state with the substituent a to tin in an axial position, may be involved94. On heating with aldehydes, the 4-benzyloxypentenylstannane shows only modest diastereofacial selectivity22. 

Treatment of allyl bromides with the complex obtained from tin(II) chloride and the disodium salt of diethyl 2,3-dihydroxybutanedioate gives an intermediate which reacts with aldehydes to provide homoallylic alcohols with 50-65% ee. Lower enantiomeric excesses were obtained with bulky aldehydes and for allylstannanes with y-substituents. Pentacoordinated allyltin complexes may be involved97. 

Allylcyciohexanone, 42,14 Allyllithium, 41, 30 from allyltin derivatives, 41, 32 reaction with 4-methyl-2-pentanone, 41,30... 

Allyltin compounds can be prepared by simple modifications of the usual reaction involving allyl Grignard reagents (139), by the 1,4-addition of trialkyltin hydrides to 1,3-dienes 140,141), or by the reaction of an aldehyde or ketone with the appropriate, tin-carrying, Wittig reagents (142). 

Allyl silanes react with epoxides, in the presence of Bp3-OEt2 to give 2-allyl alcohols. The reaction of a-bromo lactones and CH2=CHCH2Si SiMe3)3 and AIBN leads to the a-allyl lactone. " Benzyl silanes coupled with allyl silanes to give ArCH2—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCU. " Allyl silanes couple to the a-carbon of amines under photolysis conditions. ... 

Alkynes react with indium reagents such as (allyl)3ln2l3 to form dienes (allyl substituted alkenes from the alkyne). Allyltin reagents add to alkynes in a similar manner in the presence of ZrCU Alkylzinc reagents add to alkynes to give substituted alkenes in the presence of a palladium catalyst. ... 

In basic aqueous media, a kinetic study of the reaction between stannate(II) ions and alkyl halide shows that mono- and disubstituted organotin compounds are formed (Eq. 6.12a).27 The monosubstituted organotin compound is obtained after a nucleophilic substitution catalyzed by a complexation between the tin(II) and the halide atom. The disubstituted compound results from an electrophilic substitution coupled with a redox reaction on a complex between the monosubstituted organotin compound and the stannate(II) ion. Stannate(IV) ions prevent the synthesis of the disubstituted compound by complexation. Similarly, when allyl bromide and tin were stirred in D2O at 60° C, allyltin(II) bromide was formed first. This was followed by further reaction with another molecule of allyl bromide to give diallyltin(IV) dibromide (Eq. 6.12b).28... 

Later, Torii et al. found that the tin-aluminum-mediated allylation can be carried out with the less expensive allyl chloride, instead of allyl bromide, when a mixture of alcohol-water-acetic acid was used as the solvent.77 When combined with stoichiometric amounts of aluminum powder, both stoichiometric and catalytic amounts of tin are effective. As reported by Wu et al., higher temperatures can be used instead of aluminum powder.78 Under such a reaction condition, allyl quinones were obtained from 1,4-quinones, followed by oxidation with ferric chloride. Allylation reactions in water/organic solvent mixtures were also carried out electrochemically, with the advantage that the allyltin reagent could be recycled.79... 

The nature of the organotin intermediates has been studied. It was found that when allyl bromide and tin reacted in aqueous media, allyltin(II) bromide was first formed and then was followed by the formation of diallyltin(IV) dibromide (See also Section 6.4.1, Eq. 6.12b). Either of the two organotin intermediates can react with carbonyl compounds to give the corresponding homoallylic alcohols. However, the tin(II) species was found to be more reactive than the tin(IV) species (Eq. 8.38).81... 

Formation of a bis-allylated product of 4-nitrobenzoyl chloride by the reaction with allyltrimethyltin in the presence of a benzylpalladium(ll) complex was observed by Stille and co-workers in 1983.4 Trost and King also reported allylation of aldehydes by allyltin reagents in 1990.456 However, the precise mechanism was unclear until the extended studies were performed by Yamamoto and co-workers since 1995.4S7,4S7a 4S7 Aldehydes and imines react with allyltin reagents in the presence of a palladium catalyst (Equations (95) and (96)), and imines are chemoselectively allylated in the presence of aldehydes (Equation (97)).4S7,4S7l 4 b Mechanistic studies using NMR spectroscopy proved that bis-7t-allylpalladium complex 203 is a key nucleophilic intermediate (Figure 3). 

Platinum-catalyzed allylation of aldehydes with allyltin reagents was first reported in 1995.4S7 457b,483 483a Ar0matiC) aliphatic, a,/3-unsaturated aldehydes and even cyclohexanone undergo allylation with allyltributyltins in the presence of PtClgtPP 113)2 >n THF at room temperature or higher temperature (Equations (123) and (124)). Allylplatinum species are considered to be the active intermediates on the basis of related mechanistic studies on palladium catalysis. 

Pd-catalyzed intramolecular etherification reactions of aliphatic alcohols have also been practiced in tandem with other bond-forming processes, such as a Pd-catalyzed allyltin addition to an aldehyde (Equation (32)).160 Similarly, a tandem C-N and G-O bond formation sequence occurs (Equation (33)) during the reactions of /3-amino alcohols with biscarbonates in the presence of the N,O-acetal-derived ligand 43.161-163... 

Scheme 7-16 shows that a similar synthetic route leads to the asymmetric synthesis of optically active 62. The synthesis that began from homochiral aldehyde (—)-52 used this newly discovered asymmetric epoxidation three times, 52 —> 58, 58 —> 68, and 68 —> 61, finishing the conversion from 52 to 61 by following a shortened route. The last chiral center to be built is C-27, and the addition of allyltin to the aldehyde derived from 61 proceeds with high stereoselectivity to give the chiral aliphatic segment 62. 

An interesting approach to carbobicyclic polyhydroxylated compounds was proposed by Jarosz.43 It was based on a Lewis acid transformation of sugar allyltins 82 into dieno-aldehydes 83 with the fi-geometry across the internal double bond exclusively. The Wittig-type reaction of 83 afforded a triene, which underwent cyclization under high pressure, providing derivatives of bicyclo[4.3.0]nonane 84. Alternatively, dienoaldehyde 83 was converted into the phosphonate 85, which afforded the bicyclo[4.4.0]-decene derivatives (86) upon reaction with an aldehyde and simultaneous cyclization of the resulting triene.43 (Fig. 29). 

Sugar allyltins (mentioned already in 2.2.3.) were used for the preparation of higher carbon sugars. This may be illustrated by reaction of the furano-side 99 with di-O-isopropylidene-D-arabinose performed under high pressure, which provided compound 100 (Fig. 33).43,48... 

Allyltin chlorides, allylSnIL/T-, are more reactive in carbonyl addition than are the allyltrialkylstannanes, allylSnRj, and for this purpose, the latter can be converted into the former by the Kocheshkov redistribution reaction with BuSnCl3 or S11CI4 the /ra r-stannylation can be carried out with the carbonyl compound in situ in a one-pot process (Equation (97)).270... 

Tin(IV) halide-catalysed reactions of 4-, 5-, and 6-alkoxy(alk-2-enyl)stannanes exhibit 1,5-, 1,6-, and 1,7-asymmetric induction, respectively. For example, 4-substituted (pent-2-enyl)stannanes (56) give e-hydroxy derivatives (57) with a syn anti ratio of >30 for hydroxy and benzyloxy substrates (i.e. R = OH, OCH2Ph). A key allyltin trichloride intermediate has now been identified, and the transition states for its reaction with aldehyde have been calculated as being over lOkcalmol" apart for the alternative product stereochemistries. ... 

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