Tris(trimethylsilyl)silane (TTMSS)

(A) Recently, Gandon et al. have reported a novel approach to 2,4-disubstituted piperidines.11 This strategy involved the radical cyclization of 7-substituted 6-aza-8-bromooct-2-enoates. Cyclization with TTMSS and azobisisobutyronitrile (AIBN) led to trans piperidines with diastereomeric ratios of up to 99:1 in particular cases. (Chemical Equation Presented) (B) Various propiolate esters and TTMSS without solvent were stirred at room temperature overnight to give β-silicon-substituted Z-alkenes in high yields.12 Interestingly, in CH2Cl2, the reaction of propiolate ester and TTMSS in the presence of Lewis acid AlCl 3 at 0°C afforded exclusively the α-silicon-substituted alkenes. The regioselectivity observed was explained by two competitive mechanisms: a free radical and an ionic one. (Chemical Equation Presented) (C) Braslau et al. reported an efficient strategy for the preparation of N-alkoxy amines.13 Alkyl halides (X = Cl, Br) were treated with TTMSS in the presence of tert-butyl hyponitrite (TBNH) in combination with various nitroxides to allow the clean generation of N-alkoxy amines that are inaccessible by standard methods. The resulting products can be used as initiators in free radical polymerization. (Chemical Equation Presented) (D) Maulide and Markov reported a new strategy that involves a TTMSS-mediated cyclization to generate functionalized bicyclo[3.n.0]lactones in high yields.14 A Thorpe-Ingold effect induced by the ketal substituent facilitates the radical-mediated cyclization. Importantly, the contiguous stereogenic centers were generated with complete diastereocontrol. (Chemical Equation Presented) (E) The radical addition of dialkyl selenophosphates and selenophosphorothioates to electron-rich alkenes was described by Lopin et al.15 The corresponding adducts were generated in fair to excellent yields. AIBN and TTMSS were used as a radical initiator and a hydrogen donor source, respectively. This approach led to phosphonates and phosphonothioates, which can be interesting in the field of nucleotide analogues. (Chemical Equation Presented) (F) Free-radical-mediated cyclizative carbonylations of azaenynes were also carried out using TTMSS.16 The reactions afforded α-silylmethylene lactams having four- to seven-membered rings in good yields. The excellent E-diastereoselectivity observed in the TTMSS-mediated reaction was explained by the steric effect due to the bulky (TMS)3Si group. On the other hand, Z-selectivity of the resulting vinylsilane moiety was obtained during the analogous carbonylation using tributyltin hydride. (Chemical Equation Presented) (G) Bis(O-thioxo)carbamate derivatives of vicinal diols were reduced with TTMSS in the presence of AIBN to afford the corresponding olefins in good yields.17 Ribonucleoside analogues of adenosine, guanosine, inosine, cytidine, and uridine were prepared using this approach. (Chemical Equation Presented) (H) The reaction of TTMSS with the α-diazo ketones was carried out at 60°C in benzene in presence of tert-butyl hyponitrite to give the corresponding α-silyl ketones. 18 It is important to note that the α-silyl ketone does not isomerize to the more stable silyl enol ether under the reported reaction conditions. (Chemical Equation Presented). © Georg Thieme Verlag Stuttgart.