Epoxides azidotrimethylsilane

N3)2Ti(0-i-Pr)2 (l) 10 azidohydrins. Azidotrimethylsilane reacts very slowly in the presence of Ti(0-/-Pr)4 with epoxides to form azidohydrins. The reaction is more rapid when catalyzed by 1. Actually 1 is a superior reagent for cleavage of 2,3-epoxy alcohols.11 Examples ... 

Azido alcohols.1 This azide is considerably more reactive for cleavage of epoxides than azidotrimethylsilane, which requires a Lewis acid promotor. Although DMF enhances the reactivity of the silyl azide, it lowers the reactivity of the stannyl azide. The reactivity of the latter azide is also decreased by neighboring ester, acetonide, or ether groups. 

The epoxide is also opened at C-3 by various electrophilic reagents that fit into the generalized scheme in eq 3. Examples include Chlorotrimethylsilane (TMSCl) (85%), TMSCl/NaBr (X = Br) (85%), Cyanotrimethylsilane (91%), Azidotrimethylsilane (83%), Thionyl Chloride (70%), H2NCOCI (96%), and MeCH=CHCOCl (80%). The only report of unusual selectivity for opening the epoxide at C-2 was for Sulfuryl Chloride (eq 4). ... 

Halide and Azide Anions. These also open the epoxide re-gioselectively at the C-3 position. Addition of Li2CuBr4 results in bromide addition at the C-3 position of rac-(l), forming 3-bromo-1,2-propane 1-0-tosylate in 70-76% yield in THF or acetonitrile at It, or 1,3-dibromo-2-propanol in 82% yield in refluxing acetonitrile. Hydrofluorination takes place with KHF2 under solid-liquid phase transfer conditions, but the yield of fluorohydrin is very low (eq 3). Azidotrimethylsilane adds in the presence of a Lewis acid catalyst (eq 3). Addition of cyanide ion is achieved by using Diethylaluminum Cyanide in toluene. ... 

Epoxide openings performed with azidotrimethylsilane and di-ethylaluminium fluoride in dichloromethane afforded 3-azido-1,2-diols with good stereo- and regio-selectivities (C2 N2 C2-N2 83 17... 

In combination with methanol, azidotrimethylsilane was used to generate hydrazoic acid situ, and this in turn was responsible for ring opening of chiral epoxides derived from the tartaric... 

Starting materials, like 141, which are accessible from alkenes by azido-selenenylation, afforded only in a few cases vinyl azides exclusively as shown by the example 141 142 (Scheme 5.19). In most cases, after oxidation of the vicinal phenylseleno azides and elimination reaction on the intermediate selenoxide, mixtures of allyl and vinyl azides were obtained. Ring opening of trialkylsilyl-substituted epoxides was utilized several times for stereoselective synthesis of vinyl azides. Thus, treatment of the frani -contigured oxiranes 143 with azidotrimethylsilane and boron trifluoride etherate yielded cis-conflgured products 145. This result was explained by the intermediate 144 which should undergo anti-elimination. On the other hand, when subjected to sodium azide in dimethylformamide, epoxides 146 were transformed into vinyl azides 148 via... 

Miscelleneous Applications. The method of choice for the regioselective opening of benzylic and tertiary epoxides with alcohols (eq 13) appears to be a reaction mediated by organ-otin phosphate condensate (OPC) , which is readily prepared from DBTO and tributyl phosphate. DBTO catalyzes rearrangement of 3-hydroxy-2-oxo carboxylic acid esters (eq 14), a reaction reminiscent of a similar one mediated by the enzyme reductoisomerase. DBTO has been used as a catalyst for the addition of Azidotrimethylsilane to nitriles for the production of tetrazoles (eq 15). 

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