Stannyl Table

This catalyst was successfully applied to the Diels-Alder reaction of propargyl aldehydes as dienophUes [12] (Scheme 1.21, Table 1.8). Though 2-hutyn-l-al and 2-oc-tyn-l-al are unreactive dienophUes, silyl- and stannyl-suhstituted a,/ -acetylenic aldehydes react with cydopentadiene readily in the presence of 20 mol% of the catalyst at low temperature to give hicyclo[2.2.1]heptadiene derivatives in high optical purity these derivatives are synthetically useful chiral building blocks. 

TABLE 8. Absolute rate constants for the addition of triethylsilyl, tri-n-butylgermyl and tri-ra-butyl-stannyl radicals to alkenes18a... 

In the first systematic study on nucleophilic substitutions of chiral halides by Group IV metal anions, Jensen and Davis showed that (S )-2-bromobutane is converted to the (R)-2-triphenylmetal product with predominant inversion at the carbon center (Table 5)37. Replacement of the phenyl substituents by alkyl groups was possible through sequential brominolysis and reaction of the derived stannyl bromides with a Grignard reagent (equation 16). Subsequently, Pereyre and coworkers employed the foregoing Grignard sequence to prepare several trialkyl(s-butyl)stannanes (equation 17)38. They also developed an alternative synthesis of more hindered trialkyl derivatives (equation 18). 

Crotonic esters and certain homologues, when converted to their enolates with LDA and treated with stannyl and germyl chlorides, afford the y-metallo derivatives (Table 10)57. In contrast, silylation of these enolates leads to the 0-silyl derivatives. Interestingly, the halostannane derivatives show a strong preference for the (Z) geometry suggestive of a donor-acceptor interaction between the carbonyl oxygen and the electropositive tin atom,... 

Bis(stannyl) dicarboxylates 10 and 11 showed usually tetracoordinated Sn atoms by IR and MOssbauer spectroscopy. See also Tables 5 and 8124. 

Dialkyldichlorostannanes undergo reduction to dialkylstannanes (100), as shown in reaction 26. Product 100 is a good dehalogenation reagent for more complex stannyl chlorides, such as compound 32 (see Table 5) yielding compound 19 (see Table 2)134. 

Further evidence for the above-mentioned mechanism of HOMO elevation by group 14 elements is provided by studies of thioethers. The decrease in oxidation potential of silyl ethers as compared to ethers is not realized in the case of a-silylthioethers whereas a-stannyl substituents in thioethers cause a considerable cathodic shift in oxidation potential. Moreover, the effect is geometry-dependent. Values for substituted cyclic dithianes 15 are summarized in Table 21. The difference between Si and Sn in this case is illustrative. The lone nonbonding pair in the 3p orbital of sulfur is much too low in energy compared to... 

Sn—C bond formation is achieved by electrochemical alkylation of stannyl chlorides. The polarogram of dichlorodiphenyltin Ph2SnCl2, on mercury cathode, shows four waves having 1/2 values which are dependent on the electrolyte (see Table 26). Of these four,... 

Stannylation of various allenyltitanium intermediates can be effected with Bu3SnCl. The reaction favors the propargyl stannane regioisomers, unless the alky-nyl group is unsubstituted (Table 9.24) [12]. 

The stannyl cation in zwitterion 80 is only stabilized by side-on coordination with the remote C = C triple bond. The crystal structure of 80 revealed a pyramidalized tin center with the sum of valence angles of 351.1° (see Table XIV). The coordination of the tin atom to the C = C triple bond is unsymmetrical and the SnC distances... 

TABLE 7. Thia-[2,3]-Wittig rearrangements of stannylated precursors and i, i -acetals ... 

Lautens has developed effective palladium-catalyzed protocols for the cyclization/hydrostannylation of diynes to form stannylated dialkylidene cyclopentanes.For example, slow addition of tributylstannane to a suspension of dimethyl dipropargylmalonate and a catalytic amount of Pd(OH)2 on carbon (5 mol%) in THE at room temperature gave the corresponding stannylated cyclopentane in 95% yield as a single isomer (Table 10, entry 1). It was... 

Table 4. Synthesis of a-methylene ketones from stannyl ketones (Rev. [3])...

TABLE 6A.9. Kinetic Resolution of 3-Silyl-, Halo-, and Stannyl-Substituted Allylic Alcohols... 

Yamamoto has recently described a novel catalytic, asymmetric aldol addition reaction of enol stannanes 19 and 21 with aldehydes (Eqs. 8B2.6 and 8B2.7) [14]. The stannyl ketones are prepared solvent-free by treatment of the corresponding enol acetates with tributyltin methoxide. Although, in general, these enolates are known to exist as mixtures of C- and 0-bound tautomers, it is reported that the mixture may be utilized in the catalytic process. The complexes Yamamoto utilized in this unprecedented process are noteworthy in their novelty as catalysts for catalytic C-C bond-forming reactions. The active complex is generated upon treatment of Ag(OTf) with (R)-BINAP in THF. Under optimal conditions, 10 mol % catalyst 20 effects the addition of enol stannanes with benzaldehyde, hydrocinnamaldehyde, or cinnamaldehyde to give the adducts of acetone, rerf-butyl methyl ketone (pinacolone), and acetophenone in good yields and 41-95% ee (Table 8B2.3). 

When dienones such as 55 are subjected to the epoxidation conditions the electron-poorer C=C double bond is selectively epoxidized. The other C=C bond can be functionalized further, for example, it can be dihydroxylated, as shown in the synthesis of the lactone 56 (Scheme 10.11) [82]. Stannyl epoxides such as 57 (Scheme 10.11, see also Table 10.8, R1 = n-Bu3Sn) can be coupled with several electrophiles [72], reduction of chalcone epoxide 58 and ring opening with alkyl aluminum compounds provides access to, e.g., the diol 59 and to phenylpropionic acids (for example 60). Tertiary epoxy alcohols such as 61 can be obtained with excellent diastereoselectivity by addition of Grignard reagents to epoxy ketones [88, 89]. 

Table 24 Synthesis of phospholes with silyl and stannyl substituents...

Under the optimum reaction conditions, reactions of the 2-stannyl-1,3-dithiane derivatives 16,18,19 with various olefinic compounds were carried out and the results are shown in Table 3. 

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