Stannylation reagent

It is possible to achieve selective esterification at OH-6 in good yield even with acetyl chloride by employing low temperature in the presence of a controlled amount of acylating agent.13,93 Some tin derivatives (such as dibutyltin oxide) also show significant selectivity towards position 6 (Scheme 7).94,95 A polymer-bound stannyl reagent was also applied for the selective C-6 acetylation of... 

Trialkyltin alkoxide forms a coordination bond with a neighboring oxygen atom at the tin atom as in 34 and 35 because of its high nucleophilicity. Therefore intramolecular coordination could be expected to occur when equivalent amounts of stannylating reagent (Bu3Sn)20 are employed for the reaction with 10. 

To avoid stannyl reagents, there is the possibility to synthesize the same building block in one more step. First step is the formation of the benzylidene acetal 38 at the positions C-4 and C-6 of the glucal 10. The acetal formation at C-4 / C-6 is favored because you can get a six-membered instead of a five-membered ring at the position C-3 / C-4. To form 38 benzaldehyde dimethyl acetal 39 can be used with catalytic amounts of para-toluenesulfonic acid. 

The reaction performed in the first step should already be known. How do stannyl reagents react in the presence of diols ... 

The solid-phase total synthesis of (S)-zearalenone by Nicolaou et al. (372) started with the preparation of the resins 488 and 489 from the Merrifield resin (486, Scheme 9.1). Oxidation, followed by olefination of the resulting aldehyde, gave a polystyrene vinyl resin (487), which was converted into dibutyltin chloride 488. In this process, the stannylation reagent n-Bu2SnHCl was formed in situ from -Bu2SnCl2 and n-Bu2SnH2. Reduction of 488 yielded the polymer supported tin hydride 489. 

On the other hand, the corresponding tin precursor (63) undergoes smooth cycloaddition with a wide variety of aldehydes to produce the desired methylene-tetrahydrofnran in good yields [32, 33]. Thus prenylaldehyde reacts with (63) to give cleanly the cycloadduct (64), whereas the reaction with the silyl precursor (1) yields only decomposition products (Scheme 2.20) [31]. This smooth cycloaddition is attributed to the improved reactivity of the stannyl ether (65) towards the 7t-allyl ligand. Although the reactions of (63) with aldehydes are quite robust, the use of a tin reagent as precursor for TMM presents drawbacks such as cost, stability, toxicity, and difficult purification of products. 

For example, the sensitive imidoyl chloride moiety at the C-3 position of the pyrazinone scaffold is known to vmdergo Stille reactions with a variety of tetraaryltin reagents, generating the corresponding 3-substituted pyrazi-nones (Scheme 10) [26]. Furthermore, the transition-metal-catalyzed stannyl-ation at the C-3 position is also documented in the hterature, in view of cross-couphng with a variety of alkyl and (hetero)aryl hahdes [26]. However, this strategy is completely restricted to the C-3 position, while the Cl atom of C-5 position was found to be inert under these conditions. 

Stannyl derivatives of 2ff-pyran-2-one, accessible from bromopyranones by cross coupling with organotin reagents, themselves take part in Pd(0)-catalyscd cross coupling with enol triflates. This methodology offers a new approach to steroidal pyran-2-ones <96JOC6693>. 

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

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