Stannanes reactions with

A convenient route to highly enantiomerically enriched a-alkoxy tributylslannanes 17 involves the enanlioselective reduction of acyl stannanes 16 with chiral reducing agents10. Thus reaction of acyl stannanes with lithium aluminum hydride, chirally modified by (S)-l,l -bi-naphthalene-2,2 -diol, followed by protection of the hydroxy group, lead to the desired a-alkoxy stannanes 17 in optical purities as high as 98 % ee. 

However with j3-methyl-substituted stannanes, the reaction with 2-benzyloxypropanal induced by magnesium bromide, gave predominantly the chelation-controlled cw/i-product91. 

Diallyldialkylstannanes with chiral alkyl substituents on the tin, show variable asymmetric induction in their Lewis acid catalyzed reactions with aldehydes. Using bis-(/f)-2-phenylbutyl-(di-2-propenyl)stannane, enantiomeric excesses of up to 54% were obtained via attack on the / e-face of the aldehyde96. 

The stannanes (-)-ent-12 and ( + )-ent- 3 (R = CH3) are obtained with >80% ee from the alkenyllithium (-)-sparteine complex105,107a (Section 1.3.3.3.1.1.). Hence, their titanium(IV) chloride mediated carbonyl additions are accompanied by chirality transfer and enantioface selection of opposite sense. This was demonstrated for the reaction with (5)-2-benzyloxy-propanal107b the d.r. (88 12) roughly reflects the enantiomeric composition of the stannanes. 

Various o-quinodimethanes, generated in situ from o-alkenylbenzyltributyl-stannane precursors, have been used to synthesize functionalized polycycles by Diels Alder reaction with maleic anhydride, methylacrylate, dimethylfumarate and N-phenyl maleimide in the presence of electrophiles [37] (Scheme 2.16). 

A variety of reductions designed to prepare the stannane CF3SnH3 by reaction with, e.g., LiAlH4, failed (24). In each instance, SnH4 was produced, but little CFaSnHg was isolated. 

The Stille reaction has been successfully applied to a number of macrocyclic ring closures.207 In a synthesis of amphidinolide A, the two major fragments were coupled via a selective Stille reaction, presumably governed by steric factors. After deprotection the ring was closed by coupling the second vinyl stannane group with an allylic acetate.208... 

Allylic silanes and stannanes react with various electrophiles with demetallation. These reactions can occur via several related mechanisms. Both types of reactants can deliver alkylic groups to electrophilic centers such as carbonyl and iminium. 

Another sequence involves a dibromomethyl(trialkyl)stannane as the starting material. On reaction with CrCl2, addition to the aldehyde is followed by reductive elimination.151... 

Allylic stannanes are an important class of compounds that undergo substitution reactions with alkyl radicals. The chain is propagated by elimination of the trialkyl -stannyl radical.315 The radical source must have some functional group that can be abstracted by trialkylstannyl radicals. In addition to halides, both thiono esters316 and selenides317 are reactive. 

As was mentioned above (see Section 12.13.4.2), the 1,1-organoboration of alkynylsilanes, -stannanes, and -germans with trialkylboranes and boracyclanes occurs under very mild (Sn), mild (Ge), or harsh (Si, > 100 °C) reaction conditions <1995CCR125>. Similar reactions with triallylboranes proceed in general under milder conditions in comparison with trialkylboranes and furthermore a competition between 1,1- and 1,2-allylboration often takes place... 

Chlorophenyl)-4-phenyl-l,2,5-thiadiazole 128 was prepared from 3-trifluoromethylsulfonyloxy-4-phenyl-1,2,5-thiadiazole 127 by palladium-catalyzed cross-coupling reaction with the tributyl(4-chlorophenyl)stannane (Equation 20) <1996H(43)2435>. The addition of lithium chloride improves the yield. The 3-chloro- and 3-bromo-l,2,5-thiadiazole derivatives were also reactive, but only the bromo compound gave the product in comparable yield (see Section 5.09.7.6). 

A second route to nonracemic /-oxygenated allylic stannanes utilizes an enantioselective deprotonation of allylic carbamates by BuLi in the presence of (—)-sparteine. The configurationally stable a-lithio carbamate intermediate undergoes enantioselective S/,-2 reaction with Bu3SnCl and Mc SnCI (Scheme 28)65. Once formed, the /-carbamoyloxy stannanes can be inverted by successive lithiation with. s-BuLi and stannation with R3SnCl (Scheme 29)65. The former reaction proceeds with S/.-2 retention and the latter by Sf2 inversion. Nonracemic allylic carbamates can also be used to prepare chiral stannanes. Deprotonation with. s-BuLi TMEDA proceeds stereospecifically with retention (Scheme 29)65. 

Hydroxy stannanes can be prepared by cleavage of epoxides with BusSnLi or cleavage of epoxy stannanes with organocuprates (equation 33)72. The two methods are stere-ochemically complementary. The higher order cyanocuprate, Bu3Sn(Bu)Cu(CN)Li2, also affords /1-hydroxy stannanes by reaction with epoxides54. 

Trialkyl(2-borylvinyl)stannanes react with sulphur bis(trimethylsilylimide) to yield heterocyclic ylide compounds, as shown in reaction 21277. 

Reactions with participation of the C=C bond are the most studied of INOCs. Normal products of such reactions are annulated isoxazolines. A synthesis of bicyclic isoxazolines via sequential Michael and intramolecular 1,3-dipolar additions (403) are mentioned as an example. Michael addition of 1-nitroalkadiene, R1R2C=CH(CH2) CH=CHN02 to allylic stannane R3R4C=C(R5)CH2SnR63... 

The product possesses a homoallylic stannane moiety, which can be utilized as a useful synthon for cyclopropane formation (Scheme 68). Upon treatment of the homoallylstannane with HI, destannative cyclization takes place to give cyclopropylmethylsilane.271,272 A Lewis acid-catalyzed reaction with benzaldehyde dimethyl acetal affords vinylcyclopropane.273... 

A 1,3-dipolar cycloaddition of the nonstabilized azomethine ylide 6 is the key step in a three-component reaction. The azomethine ylides were generated from (2-azaallyl)stannanes or (2-azaallyl)silanes 5 through an intramolecular iV-alkylation/demetallation cascade. The ylides underwent cycloaddition reactions with dipolarophiles yielding indolizidine derivatives 7-9 <2004JOC1919> (Scheme 1). 

The reaction of the stannane (176) with phosphorus trichloride gives the phosphorin (177). The electron-donating methyl group reinforces the ring dipole, the negative end of which is the phosphorus atom.189 The dibenzo analogue (178) has also been prepared and its electronic structure studied by photoelectron spectroscopy.160... 

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