Geminal diacetates

The allylic geminal diacetate 141 undergoes the monoallylation of malonates to give 142 and the two regioisomers 143 and 144[93,94]. The dimethylacetal 145 or ortho esters of aromatic and a,/3-unsaturated carbonyl compounds react with trimethylsilyl cyanide to give the methyl ether of cyanohydrin[95]. 

Acylals (geminal diacetates) are frequently used as protecting groups for aldehydes because of their stability to neutral and basic conditions [8]. In addition, the acylal functionality can be converted into other useful functional groups [9]. For example a novel synthesis of chiral allylic esters has been developed using palladium-catalyzed asymmetric allylic alkylation of gem-diesters [10]. The allylation of... 

This method has also been applied to unsymmetrical acyclic allyl esters. The reaction of an azlactone with a geminal diacetate substrate gave access to an advanced intermediate for the synthesis of sphingofungin F. ... 

Kabalka and co-workers have shown that an attenuated form of BI3, BI3 NEt2Ph, will cleave a variety of compounds containing C-O single bonds at elevated temperatures [20]. Solutions of this reagent are prepared by reacting the commercially available amine-borane complex with I2 in benzene at 80 °C for several hours. This reagent cleaves ethers [21], esters [20], and geminal diacetates [21]. Esters [20] are cleaved to an activated acyl intermediate RCOX which can be used to prepare acids, other esters, and amides (Eq. 10). 

The fact that ketones, aldehydes and geminal diacetates are readily available from these reactions illustrates their complementarity to reactions with allylsilanes. Specifically, the equivalency of allylic ethers to homoenolates allows for the formation of compounds extended... 

In exceptional cases, addition of nucleophiles across nonactivated alkenes bearing a leaving group gives electrophilic cyclopropanes. An example is the reaction of an allylic geminal diacetate with tetramethyl ethane-1,1,2,2-tetracarboxylate in the presence of a palladium catalyst which gives the cyclopropane tetracarboxylate derivative 11. ... 

Scheme 12.22 Asymmetric allylic alkylations of geminal diacetates [42].

When an aldehyde is treated with acetic anhydride/anhydrous iron(ni) chloride, geminal diacetates are formed in good to excel-... 

However, if 1.5 equiv of cobalt(II) chloride is added, the geminal diacetate is formed (eq 58). ... 

When an aldehyde is treated with acetic anhydride/anhydrous iron(III) chloride, geminal diacetates are formed in good to excellent yields. Aliphatic and unsaturated aldehydes can be used in this reaction as shown in eqs 54-56. Interestingly, if an a-hydrogen is present in an unsaturated aldehyde, elimination of the geminal diacetate product gives a 1-acetoxybutadiene. 

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