Allyltin also

Allyltins also react with similar substrates such as pyridines or pyridiniums selectively to the a position [271]. An enantioselective approach was done with a chiral acyl chloride as activator and enantioselectivity inductor [272]. This approach was applied to heterocydes such as /3-carboline, leading to both enantiomers depending on the nature of the allyltin engaged in the reaction (Scheme 6.31) [273]. Similarly, oxazolidinones were used as chiral auxiliaries, to promote the synthesis of chiral 1,4-dihydropyridines [274]. 

Allyltin compounds can also be formed by elimination from the tin derivatives of allyldialkylcarbinols (145). 

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... 

Tin compounds can be produced by the Nalco-type reactions39 as well as by Cd and Zn mediated methods42,43. The use of organotin compounds in electrodically induced transmetallations has also been described in a study in which Grignard-type allylation of carbonyl compounds has been carried out by electrochemically recycled allyltin reagents44. 

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). 

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... 

Alkoxides that arise from simple carbonyl additions have also functioned as excellent in situ nucleophiles for intramolecular hydroalkoxylation reactions. Garbinols derived from the addition of allyltin reagents have proved to be potent nucleophiles in reactions of this type (Equation (99)),349 and this approach has also been used for the combined addition-cyclization of alkynals under Pd(n)350 or Cu(i)351 catalysis, and alkynones under Pd(n) catalysis.352... 

Stereoselective addition of allyl metal reagents to various functionalities is an important reaction in organic synthesis [32, 33]. The allylation of epoxides and aziridines with allyltin reagent is catalyzed by Lewis acids. Even though many Lewis acids have been reported to catalyze this reaction, Bi(OTf)3 is distinct because it avoids the formation of byproducts and is also environmentally more compatible. It catalyzes the reaction of aryl epoxides with tetraallyltin to afford the corresponding homoallyllic alcohol [34]. 

Allyltriphenyltin can also be prepared by using the reaction of preformed allylmagnesium bromide with triphenyltin chloride.2 However, the submitters prefer the simpler procedure described above for large-scale preparations of allyltin compounds. 

The acidolysis of allenyltins was later investigated by Kuivila and Cochran15. Although these acidolyses formally involve substitution at unsaturated carbon, rather than at saturated carbon, it is of interest to compare them with the allyltin cleavages, and details are also given in Table 5. The overall rate coefficients for acidolyses were partitioned into their SE2 and SE2 components by determination of the proportions of allene and acetylene, e.g. 

Free-radical-mediated four-component coupling reactions are rare. However, when an allyltin-mediated radical carbonylation is conducted in the presence of electron-deficient alkenes, four-component coupling reactions take place efficiently to give good yields of p-functionalized <5,fi-unsaturated ketones [40]. The wide scope of this four-component coupling reaction is noteworthy Primary, secondary, and tertiary alkyl bromides and iodides can be used as well as aromatic and vinylic halides. A variety of electron-deficient alkenes, such as methyl vinyl ketone, ethyl acrylate, acrolein, acrylonitrile, and vinyl sulfone, can be used as the acyl radical trap (Scheme 6.23). Fluorous allyltin compounds can also be used in four-component coupling reactions [41]. 

The allylation of carbonyl compounds with allyltin reagents is still an active area of organotin chemistry from the methodological point of view, and also for synthetic applications. For completeness we should add several alternative techniques, such as the development of trifluoromethanesulphonic acid as a Bronsted acid catalyst for the allylation of aldehydes in water123, or the design of fluorous allyltin reagents for the platinum-catalysed allylation of aldehydes124. 

A polymer-supported allyltin derivative was also reported to undergo a Lewis-acid-catalysed addition to benzaldehydes to give products such as l-phenylbut-3-en-l-ol and 1 -(p-bromophenyl)but-3-en-1 -ol154. 

Allyltributyltin can be used in combinatorial radical allylation. Moreover, a polymer-supported reagent bearing an allyltin group was also developed and it can be used for the radical allylation of alkyl halides. 

Aryl- and heteroaryltins are similarly used for the synthesis of the corresponding iodides, and they also allow the presence of functional groups such as alcohols , esters and amides and amines . It is noteworthy that with substrates such as allyltins or propargyltins the iododestannylation occurs with rearrangement of the unsaturation . ... 

Cross-coupling ofallyl bromides with allyltins (cf. 10, 26). The coupling of prenyl bromide with the tin reagent 1 in the presence of 10% ZnCh gives myrcene (2) in high yield. This coupling also provides a synthesis of vitamin K, (3). ... 

Bis(allyl)Pd and -Pt compounds are also made by treatment of PdClj and PtClj with RMgX see Table 4. Mixed bis(allyl)Pd complexes can be obtained when an allylic RMgX reagent or allyltin reagent is slowly added at — 30°C to an ether dioxane solution of ( t-allyl)palladium chloride dimer . Removal of pentane under vacuum affords the products as light golden-yellow crystalline solids in 80% yield. 

Alkoxy-substituted allylstannanes are transmetalated on treatment with Sn(IV) halides to give allyltin trihalides which react with aldehydes with effective remote asymmetric induction [62]. For example, the 5-benzyloxy-4-methylpent-2-enylstan-nane gives predominantly the 1,5-anti products with useful stereoselectivity (Eq. 37) [62b]. Allylstannanes and 5-benzyloxy-4-methylpent-2-enylsilanes also react with aldehydes with modest levels of 1,5-induction after treatment with SnCU. Trans-metallation to give intermediate allyltin trihalides might be involved (Eq. 38) [63]. 

Hf(OTf)4 [or Zr(OTf)4] also acts as a catalyst in the allylation of imines with allyltri-butylstannane (Eq. 19) [23], Extension to the three-eomponent condensation of aldehyde, amine, and allyltin was made possible by use of these catalysts in the presence of a dehydrating agent, MgS04 (Eq. 20). Other Lewis acids were ineffective, because they deeompose or become deactivated by the amine and/or the water produced during imine formation. 

The controlled fragmentation of the primary sugar allyltins is a convenient method for the preparation of dienoaldehydes with the -configuration across the internal double bond. The Z-dienes are also available from sugar allyltins, but the secondary ones. When the sugar allylic mesylates (or chlorides) 86 reacted with a tin nucleophile, the Sn2 product 92 was obtained. 

Prior to the studies which uncovered the utility of organotin acylation as described in the preceding paragraphs, acid chlorides were also found to undergo a similar rhodium(I)-mediated acylation with allyltins to form p, y-unsaturated ketones. The palladium(0)-catalyzed coupling has been found to be more general with respect to varied substitution patterns of both reagents and could be conducted under essentially neutral conditions (see Section 1.13.5.1). 

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