Allyltin substituted

I.3.3.3.6.I. Unsubstituted and Alkyl- and Aryl-Substituted Allylstannanes and Allyltin Halides... 

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... 

Hexamethylditin readily adds to allene in the presence of Pd(PPh3)4 to give an allyltin compound. An unsymmetrically substituted allene such as 1,1-dimethylal-lene undergoes kinetically controlled addition at lower temperatures, whereas at higher temperatures thermodynamically more stable products are formed (Scheme 16.61) [66],... 

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. ... 

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. 

Unfortunately, substitution in the y-position, such as in crotyltin, led to poorly reactive allyltins, due to the decrease in the addition rate of the radicals to the double bond. It has been established that, generally, the competitive allylic hydrogen abstraction became predominant, destroying the crotyltin reagent548. The use of y-substituted allyltins for the photo-induced radical allylation of carbonyl compounds represents an interesting... 

Transmetallation with S11CI4 is well used for the control of regio- and stereoselectivities.128 As an example of 1,5-induction, tin(iv) chloride-promoted reactions betweeen aldehydes and alkoxy-substituted allyltins give the linear adducts l,5-ty (Z)-alkenols with excellent stereoselectivity (Equation (39)).129-133... 

It should be noted that when the reaction is conducted with a chiral aldehyde and a chiral y-substituted allyltins, a matching effect when both partners impose a convergent selectivity, or a mismatching effect when the facial selectivity is divergent, may happen . Such a stereoconvergent effect was used in the synthesis of the antitumour agent azinomycin (equation 4). 

Allyltin reagents are employed for the synthesis of Ru-allyl compounds. They are less reactive than allylmagnesium halides and can be used for the preparation of halo-substituted derivatives ... 

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]. 

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). 

The two principal routes to the organotin peroxides involve substitution by a peroxide nucleophile at a tin centre (equations 14-69 and 14-70), or (pericyclic) reaction of an allyltin compound with singlet oxygen (equation 14-71). Distannyl peroxides have also been prepared by the (homolytic) reaction of distannanes with triplet oxygen (equation 14-72). 

The use of allyltins and y-substituted allyltins in the stereocontrolled synthesis of homoallylic alcohols. ... 

In spite of their potential in substitution or in addition reactions, supported allyltins have not been used very often. Examples include radical transfer of an allyl unit to a-bromo ketones or esters, which was described for allyltins grafted on a soluble non-cross-linked polystyrene support. In this case, tin contamination for the initial reaction was 7-54 ppm but increased to 15-80 ppm when recycled polymer was used. 

Asymmetric addition of allyltins to RCHO Addition of y-substituted allylstan-nancs to aldehydes to form homoallylic alcohols can proceed in high diastcrco- and cnantioselectivity when carried out in the presence of 1 cquiv. of the Yamamoto chiral acyloxyborane 1 (16, 314). If trifluoroacctic anhydride is used as promotor, then only catalytic amounts of 1 are required. Virtually quantitative yields are obtained if 1 and (TFA)20 are used in the ratio 1 eq 1.2 eq. 

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