Allylstannanes synthesis

Stereocontrolled synthesis of polycyclic ethers and related heterocycles via intramolecular reactions of allylstannanes 97YGK619. 

Evans developed a new method for the synthesis of [(-C-allylglycosides, based on BusSnOTf-mediated ring-opening of glycal epoxides with allylstannanes as nucleophiles [81a], This methodology has been efficiently used in the (3-stereoselective introduction of the side chain (C44-C51) of spongistatin 2 (Scheme 8.43) [81b,c]. 

A useful synthesis of allylstannanes from primary alcohols involves conversion of the alcohols into their O-substituted 5-methyl carbonodithioates, thermolysis to effect [3,3] rearrangement to the corresponding 5-substituted 5-methyl carbonodithioates, and treatment with a trialkyl-tin hydride under free-radical conditions to form the allylstannane21. This procedure has been applied to the synthesis of functionalized allylstannanes including (5)-( )-4-(benzyloxy)-2-pen-tenyl(tributyl)stannane22. 

Two approaches for the synthesis of allyl(alkyl)- and allyl(aryl)tin halides are thermolysis of halo(alkyl)tin ethers derived from tertiary homoallylic alcohols, and transmetalation of other allylstannanes. For example, dibutyl(-2-propenyl)tin chloride has been prepared by healing dibutyl(di-2-propenyl)stannane with dibutyltin dichloride42, and by thermolysis of mixtures of 2,3-dimethyl-5-hexen-3-ol or 2-methyl-4-penten-2-ol and tetrabutyl-l,3-dichlorodistannox-ane39. Alternatively dibutyltin dichloride and (dibutyl)(dimethoxy)tin were mixed to provide (dibutyl)(methoxy)tin chloride which was heated with 2,2,3-trimethyl-5-hexen-3-ol40. 

The key step in the synthesis of A-ring fragment 50 [56] is the chelation-controlled addition of allylstannane 53 to aldehyde 52, which sets the C7 stereocenter and introduces the C8 gem-dimethyl moiety. Aldehyde 52 is itself prepared from 1,3-propanediol using the author s protocol for titanium-catalyzed enantioselective allylstannation [57], which sets the C5 stereocenter, followed by chelation-controlled Mukaiyama aldol addition [58] to establish the C3 stereocenter (Scheme 5.6). 

A further application of ring-closing metathesis in seven-membered heterocyclic ring formation is in the synthesis of the trans-fused oxpane systems. This process involved tandem RCM/allylstannane-aldehyde cyclizations and interaction of the process provides access to trans-fused polyoxepanes <00S883>. 

Similar reactions can be carried out by using a tin(ll) compound rather than metallic tin.264-266 The allylstannanes are still easily handled but are much more reactive than the simple alkylstannanes, and their principal modes of reaction are summarized in Scheme 8. All these reactions, and particularly the carbonyl addition reactions (X=Y = R2C=0), are important in organic synthesis, and are covered in that respect in Volume 9. Only... 

Most of the current interest, however, is directed toward the use in synthesis of the formation of a carbon-carbon bond by the addition of an allylstannane to carbonyl groups (Equation (114)). These reactions have been thoroughly reviewed,16 18 19 299-301 and are covered in Section 9.08.3 of this series, and will not be considered in detail here. 

The synthesis of the C20—C26 fragment started with a 4-alkylation of methyl aceto-acetate The first stereocentre was introduced by enantioselecuve catalytic hydrogenation with Noyort s (S)-binap rhodium complex (cf p 102f.) Stereoselective Frater-Seebach alkylation with allyl bromide introduced the second stereocentre in 90% yield (cf p 27) Stereospecifid introduction of the stereocentres C24 and C2 was achieved by a chelation controlled addition of an allylstannane to an aldehyde (see p 66f) After some experimentation with Lewis acid catalysts and reaction conditions a single diastereomer of the desired configuration was ob-... 

Tandem RCM/allylstannane-aldehyde cyclizations are successfully used for the iterative synthesis of /ra/w-fused oxepane systems, particularly, three tricycles modeling different fragments in brevetoxins and ciguatoxins <2000S883>. Grubbs catalyst <1996JA100> was used on RCM step of the tandem while the procedure similar to that proposed by Yamamoto et al. <1991TL7069> was applied on the second step. 

Recently, Yu et al. [88] and Keck et al. [89] reported the synthesis of enantio-enriched homoallyl alcohols 198. Alcohols 198 are prepared from allylstannane 197, by using chiral Ti(IV)-based catalysts [88, 89], with ees ranging from 90 to 96% (Scheme 13.70). 

Cross-metathesis of two different alkenes 11 and 42 usually produces a mixture of products 6 and 15. However, depending on the functional groups R1 and R2, the cross-product 6 is obtained with high selectivity rather than the homoproduct 15 from 11 and 42. Some terminal alkenes, such as allylstannane [16], acrylonitrile [17,18] and allylsilane [19], undergo clean cross-metathesis to give cross-products 6 as the main product, rather than homoproducts 15. Cross-metathesis of the cyclic alkenes 43 with terminal alkenes 42 can be used for the synthesis of dienes 44. 

For the reaction catalyzed by Lewis acids, see the following Fleming, I. Allylsilanes, Allylstannanes and Related Systems. In Trost, B.M., Fleming, I. (Eds.), Comprehensive Organic Synthesis. Pergamon, Oxford, 1991, Vol. 2, p. 563. 

OXAZOLIDINECARBOXYLATE has previously been described in Volume 70 of Organic Sytheses. An alternative procedure for the preparation of this compound is presented in this volume along with its use in a dia-stereoselective addition reaction with 2-TRIMETHYLSILYLTH1AZOLE to provide a compound bearing a 2-amino-1,3-diol substructure that appears in a variety of natural products. The conversion of abundantly available isosorbide into OSO ISOPROPYLIDENE-l ti-DIANHYDRO-d-GLUCITOL provides a potentially useful carbohydrate-deri ved material for the use in complex tetrahydrofuran synthesis. Finally, asymmetric reduction of an a,j9-unsaturated acylstannane with (R)-BINAL provides access to (S,E)-l-(METHOXYMETHOXY)-l-TRIBUTYLSTANNYL-2-BUTENE, an a-alkoxy allylstannane that has been used in enantioselective vicinal diol synthesis amongst other transformations. 

In 1973, it was demonstrated that 1,2-epoxystannanes, produced from vinylstannanes and MCPBA, could be isolated and characterized, in comparison widi 2,3-epoxystannanes (from allylstannanes), which are extremely reactive and have not been isolated (see Section 4.2.2.3). Subsequently, useful applications of 1,2-epoxy stannanes have been reported, including the internal alkyne ketone conversion, in the caibapenem and carbacephem 0-lactam antibiotic) skeletons. Ketone (10) should be of value in the construction of the biologically interesting l-carbapen-2-ene ring system. Synthesis of ketoacetates of potential use in the carbacephem system (e.g. 11 and 12) was also achieved by similar sequences shown in Scheme 11. ... 

Intramolecular allylation of functionalized allylstannanes is feasible. One application used in the synthesis of natural product is shown in Eq. (108) [282]. The yield is, however, moderate in this example. More examples of titanium-promoted inter- and intramolecular reactions of allylstannanes with carbonyl and related compounds are summarized in Table 10. 

Yamamoto, Y, Kobayashi, K, Okano, H, Kadota, I, Asymmetric synthesis of syn-l,2-diols via the reaction of aldehydes with chiral "y-(tetrahydropyranyloxy)allylstannanes, J. Org. Chem., 57, 7003-7005, 1992. 

The spongistatins are a family of architecturally complex bisspiroketal macrolides, which display extraordinary cytotoxicity. During the second generation synthesis of the ABCD subunit of spongistatin 1, A.B. Smith and coworkers utilized the Keck allylation to construct the Kishi epoxide. The allylation was carried out under standard conditions, using tributyl-(2-ethylallyl)-stannane as the allylstannane reactant. The desired product was formed in high yield and a diastereomeric ratio greater than 10 1. 

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. ... 

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