3-Stannyl ketones

Siloxycylopropanes corresponding to ketone homoenolates (e.g. 3) also react smoothly with SnCl at 15 °C to give 3-stannyl ketones (e.g. 14) Eq. (17) [31]. In the same manner, the 3-stannyl aldehyde 15 has been prepared in good yield. Eq. (18). 

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

Phenylhydrazones of /i-stannyl ketones undergo oxidative radical cyclization to afford azocyclopropanes upon treatment with an oxidizing agent such as DDQ, Pb(OAc)4 and NBS (equation 27)43. 

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). 

Oximes derived from p-silyl and P-stannyl ketones undergo unusual Beckmann rearrangement, giving rise to nitriles as predominant products. For example, Beckmann rearrangement of 3-trimethylsilylcyclohexanone oxime 88 (Scheme 15) proceeds to the formation of the acyclic alkenyl nitrile 89 as the major product.90 The nitrile is believed to be formed by fragmentation of the protonated oxime, giving the P-silyl—stabilized cation 90, followed by desilylation. Our... 

Radical reaction mechanisms of and at organic germanium, tin and lead 595 B. Photolysis of a-Stannyl Ketones... 

However, the instability of the simplest a-tin ketones precludes the application of CIDNP methods in studying their reaction mechanisms. Me3SnCOMe decomposes on attempted isolation if exposed to daylight. Therefore, to study the mechanisms of the photodecomposition of R3SnCOR it is reasonable to choose more steric hindered derivatives which are relatively stable under ambient conditions. Consequently, the regularities of the reaction mechanisms of a-stannyl ketones R3SnCOR have been studied with 2-methylpropanoyltripropylstannane" Pr3SnCOCHMe2 (9). 

Addition of BuiSnLi to cyclohex-2-enone followed by enolate trapping with n-decyl iodide proceeded with high diastereoselectivity to provide the 2,3-rrdiR5-stannyl ketone (16), which could be equilibrated with the cis diastereomer (17) upon treatment with base. LAH reduction, followed by separation of the diasteteomers, afforded samples of the 2-alkyl-3-stannylcyclohexanols as shown in Scheme 17. Iodine(III)-mediated fragmentation was shown to proceed in a stereospecific anti manner, with either of the rrdiRr-2,3-cyclohexanols affording ( )-enal (18), and the cir-2,3-alcohol the (Z)-enal (19 Scheme 17). Enal (18) was then utilized in a stereoselective synthesis of the mosquito pheromone, erythro-6-asx-toxyhexadiecan-S-olide (20 Scheme 18). ... 

The conjugate addition of bis(trimethylstannyl)lithiocuprate to an a,/ -unsaturated ketone yields only one diastcrcomcr of the 3-stannyl ketones 1 and 2 resulting from axial 1,4-addition1. 

In 2003, Baba and coworkers reported first examples of a catalytic Michael addition of stannyl ketone enolates (129) to a, S-unsaturated esters (131) using a catalytic amount of tetrabutylammonium bromide (equation 38) . Their investigations showed that the... 

TABLE 9. Michael additions of stannyl ketone enolates catalyzed by Bu4NBr (equation 38)... 

Sterically unhindered enones may produce mixtures of products, including carbon stannylated species. For example, methyl vinyl ketone gives rise to significant quantities of the inverted 1,4-adduct, where tin binds at the 4-position, leading to a p-stannyl ketone. In the case of methyl propenyl ketone, addition occurs at positions 3 and 4, producing an a-stannyl ketone (Scheme 48). 

Yasuda, M., Chiba, K., Ohigashi, N., Katoh, Y., Baba, A. Michael Addition of Stannyl Ketone Enolate to a, 3-Unsaturated Esters Catalyzed by Tetrabutylammonium Bromide and an ab Initio Theoretical Study of the Reaction Course. J. Am. Chem. Soc. 2003, 125, 7291-7300. 

Enol siiyl ethers undergo Pd-catalyzed coupling with aromatic bromides in the presence of tributyltin fluoride, which converts the enol silyl ethers into the stannyl ethers or a-stannyl ketones regarded as real active species chemoselective a-arylation of terminal ketones is possible (equation 110). ... 

The acyltrialkylstannanes are readily hydrolysed to the parent aldehydes, and are oxidised in the air to give the corresponding carboxylates, R3SnOCOR 63 in a radical chain reaction which presumably is similar to that of the autoxidation of an aldehyde, and involves as a key step the Sh2 reaction of an acylperoxyl radical at tin rather that at hydrogen (equation 6-26). The trialkylstannyl peroxyester which is formed then reacts with the parent stannyl ketone to give the trialkyltin carboxylate. 

The preparation of enantioenriched Q -(alkoxy)allylstannanes has been advanced by the asymmetric Noy-ori reduction of the stannyl ketone 264 with 2,2 -dihydroxy-l,T-binapthyl lithium aluminum hydride (BINAL-H) reagents affording the non-racemic (5 )-265 with > 95% ee, upon O-alkylation with common protecting groups (Scheme 5.2.57, top). °... 

Organotin radicals, and some related species, add to the carbonyl oxygen of cyclopropyl ketones 1 to produce a,a-disubstituted cyclopropylmethyl radicals. j -Scission, followed by hydrogen transfer with the organotin hydride, yields a mixture of enolates and isomeric a-stannyl ketones. Although the enolates can be isolated, they are usually hydrolyzed in situ with methanol to give the corresponding ketones 3. 

On consecutive deprotonation and Sn-Li exchange with a -stannyl ketone, Ryu... 

An open chain example44 153 of asymmetric homoenolates from allylic amines uses the proline derivative 152 and the p-stannyl ketone 153 made by conjugate addition of Bu3SnLi to the enone 150. 

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