Aldehydes allylstannane

The stereoselectivity of the boron trifluoride induced reactions was initially discussed in terms of open-chain, antiperiplanar transition states66. However studies of Lewis acid induced intramolecular allylstannane-aldehyde reactions are supportive of a synclinal process56,67. 

With 2-butenyl- and 3-phenyl-2-propenylstannanes coupling of this Cram selectivity with the intrinsic stereoselectivity of the Lewis acid induced allylstannane-aldehyde reaction gives useful stereocontrol at three contiguous stereogenic centers66,81. 

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>. 

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. 

A thorough mechanistic study of the intramolecular allylstannane-aldehyde cy-clization has recently been reported [75b]. The intramolecular cyclization substrates described allow the double bond geometry of the allylstannane to be varied. The Lewis acid-promoted cyclization of either the E- or Z-stannane can lead to the four limiting stereoisomeric products (Scheme 10-41). 

Analogous reactions of more complex allylstannanes have been applied to natural product synthesis72, although /(,/i-dialkylated aldehydes appear not to react, possibly due to deactivation of the aldehyde towards nucleophilic attack72. 

In contrast to this generally high preference for. tyn-products for boron trifluoride mediated reactions between 3-a//c v/-Substituted allylstannanes and aldehydes, //-products are preferred for reactions involving 3-p/ cn>7-substituted allylstannanes. This stereoselectivity was observed for a range of aldehydes, and was explained in terms of the increased propensity for the tin-allylie carbon bond to be polarized when the -substituent is able to stabilize a positive charge so favoring a cyclic transition state73. 

Good Cram selectivity is observed for Lewis acid induced reactions between allylstannanes and aldehydes with alkyl-substituted a-chiral centers66,87. This enhanced Cram selectivity may be due to the effect of the Lewis acid on the trajectory of nucleophilic attack on the aldehyde66. 

Effective 1,7-asymmetric induction was observed in the analogous reactions between C-hydroxy-allylstannanes and aldehydes, although in this case the free hydroxy group was required126. 

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. 

As with other noncatalyzed reactions of allylstannanes with aldehydes (see Section 1.3.3.3.6.1.3.2.) these reactions are believed to proceed via a chair-like six-membered ring transition state in which the a-substituent, in this case methoxymethoxy, adopts the axial position103. 

AUylzirconium complexes are conveniently obtained by the regio- and stereoselective hydrozirconation of allene [127-133] and can be, for example, used subsequently for the MAO-catalyzed allylzirconation of alkynes to prepare enyne derivatives [132]. Alternatively, the preparation of (E)-l,3-dienes from aldehydes and the appropriate allylstannane zirconocene derivative (R = SnBu,) is accomplished (Scheme 8-17) [131], Note that addition of [Cp2Zr(H)Cl[n (1) on the aUenyl reagent with the... 

Use of di-( -butyl)stannyl dichloride along with an acyl or silyl halide leads to addition of allylstannanes to the aldehydes.1728,172 Reaction is also promoted by butylstannyl trichloride.173 Both SnCl4 and SnCl2 also catalyze this kind of addition. 

Allylstannane additions to aldehydes can be made enantioselective by use of chiral catalysts. A catalyst prepared from the chiral binaphthols R- or S-BINOL and Ti(0-i-Pr)4 achieves 85-95% enantioselectivity.187... 

The indium-mediated allylation carried out with allylstannanes in combination with indium chloride in aqueous medium was reported by Marshall et al.113 Allylindium was proposed as the reaction intermediate. Various aldehydes can be alkylated very efficiently with 3-bromo-2-chloro-l-propene mediated by indium in water at room temperature. Subsequent treatment of the compound with ozone in methanol followed by workup with sodium sulfite provided the desired hydroxyl ester in high yield.114... 

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). 

Conversion of the A-ring aldehyde 50 to hydroxyallylsilane 57 is accomplished in a three-step sequence involving addition of allylstannane 49 followed by oxidation-reduction for diastereomeric enrichment at Cll. With both hydroxyallylsilane 57 and aldehyde 51 in hand, intermolecular Prins pyran annulation proceeds smoothly to furnish the tricyclic compound 58 in 61 % isolated yield. 

Allylstannanes undergo diasterospecific additions to chiral a-alkoxyaldehydes, as shown in reaction 45295. Stereospecific additions to aldehydes are attained in the presence of... 

A case of the addition of an allylstannane to aldehydes has been reported by Tagliavini to proceed with appreciable enantioselectivity (Scheme 6.15) [40]. A notable feature of the Zr-catalyzed transformations is that they proceed more rapidly than the corresponding Ti-catalyzed processes reported by the same research team (see Scheme 6.16). Furthermore, C—C bond formation is significantly more efficient when the reactions are carried out in the presence of 4 A molecular sieves the mechanistic rationale for this effect is not known. It should be noted that alkylations involving aliphatic aldehydes are relatively low-yielding, presumably as the result of competitive hydride transfer and formation of the reduced primary alcohol. 

Scheme 6.15. Zr-catalyzed enantioselective addition of allylstannanes to aldehydes is more facile than the corresponding Ti-catalyzed processes.

D. P. Curran, s. Hadida, M. He, Thermal Allylations of Aldehydes with a Fluorous Allylstannane. Separation of Organic and Fluorous Products by Solid Phase Extraction with Fluorous Reverse Phase Silica Gel , /. Org. Chem. 1997, 62, 6715. 

Homoallylic alcohols can readily be prepared from commercially available tetraallytin and acetals or aminoacetals in the presence of trifluoroacetic acid on silica gel this provides an alternative to the reaction of an allylstannane with an aldehyde.278 By a similar mechanism, homoallylic peroxides can be prepared from monoperoxyacetals (Equations (99) and (100)).279... 

The catalytic activity of the trityl moiety was unobjectionably adjusted in the addition reaction of the allylstannanes to aldehydes [148]. In this allylation process the trityl chloride 52, due to its disposition to partially ionic character of the halogen bonding, was employed as a catalyst in the complementary tandem with weak Lewis acid TMSCl (Scheme 57). The excess of the silyl component was necessary in order to release the trityl catalyst from the intermediate to complete the catalytic cycle. The achieved yield was 93%, when trityl chloride 52 was used. 

The titanium(IV) chloride catalyzed reaction of allylstannane 22 and aldehyde 23 to give a 3.5 1 mixture of adducts 24 and 25, which is related to example . Here again, two stereogenic centers (a and b) are created and the relative disposition of the substituents at positions a and b (syn or anti), and with respect to the configuration of the starting materials, had to be determined (see pp465 and 474)119. 

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-... 

Asymmetric catalysis of BINOL-Ti complexes in the reaction of aliphatic and aromatic aldehydes with an allylstannane has also been reported independently by Umani-Ronchi [54] and Keck [55]. The former group has suggested that a new complex generated by the reaction of the BINOL-Ti complex with allylstannane is the catalytic species that provides remarkably high enantioselectivity (Scheme 8C.23). It is interesting that no reaction occurs if dry MS 4A... 

The obtention of this very labile product, containing an allylstannane and an aldehyde in the same molecule, was tried unsuccessfully using many oxidizing conditions. Eventually, this product could be prepared following a Mukaiyama oxidation. The basic conditions were essential to avoid protiodestannylation. The product could not withstand chromatography... 

Methanol promotes addition of allylstannanes to aldehydes and ketones, to give homoallylic alcohols without added catalyst.86 Aldehydes are significantly more reactive. It is suggested that the primary activating influence is hydrogen bonding to the carbonyl. 

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

Regio- and stereo-selective allylation of sulfonylimines has been carried out with trifluoro(allyl)borates and allylstannanes, using palladium-pincer complexes as catalysts.47 Syn products predominate, in contrast to the corresponding reaction of aldehyde electrophiles DFT calculations have been employed to probe the mechanistic differences. 

Chiral (salen)chromium(III) complexes catalyse the asymmetric allylation of a range of aldehyde types, using allylstannane reagents.171... 

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