1.2- Diols, reaction with dialkyltin oxides

The formal tin counterpart of the dioxolanes formed from vicinal diols by reaction with ketones are stannylenes, formed by reaction with dialkyltin oxides. The commonest reagent is dibutyltin oxide, Bu2SnO, which converts diols to stannylenes when refluxed in an aprotic solvent such as benzene, with continuous distillation out of the water generated. The partly ionic nature of... 

Two types of tin derivatives have been used mainly to achieve these reactions dialkylstannylene acetals are formed by reaction of dialkyltin oxides with diols tributyltin ethers are formed by reaction of bis(tributyltin) oxide with alcohols. Some aspects of the regioselectivity achieved with these two types of intermediates are the same, while others are different, as will be outlined in the sections to follow. Where the reaction outcomes are similar, the dialkyltin reagents are strongly preferred because of their lower toxicity. As these reagents are heavily employed, the topic has been reviewed several times, but siguilicant uew observatious continue to be made. This chapter is not intended to be a comprehensive summary of all applicatious of these intermediates, but will highlight examples of each type of selectivity. 

The 1,3,2-dioxastannolanes are important in organic synthesis because they can readily be derived from dialkyltin oxide and 1,2-diols, as in carbohydrates the reaction can be carried out in toluene in a few minutes under microwave irradiation.387 The dioxastannolanes can then be subjected to regioselective reaction with an electrophile such as an acyl chloride (Equation (140)) or sulfonyl chloride, or an isocyanate. The acylation or sulfonation can be carried out with catalytic amounts of the dialkyltin oxide, including the recoverable (C6F13CH2CH2)2Sn0.388... 

The 1,3,2-dioxastannacycloalkanes can be prepared by the usual routes to organotin alkoxides, but whereas simple alcohols react with diorganotin oxides only to the stage of the distannoxanes (R 0)R2Sn0SnR2(0R ), 1,2-diols react further to give the dioxastannolanes (equation 14-41).61 62 The reactions proceed much more quickly (typically in 4 to 9 min) if the reactants are heated in a microwave oven.63 Similar reactions can be carried out with dialkyltin dihalides64 and, under milder conditions, with dialkyltin dialkoxides.65-67... 

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