The Acid-Induced Rearrangement of 1-Hydroxyalkyltris(trimethylsilyl)silanes

Abstract

In the presence of strong acids, such as HCl or H2SO4, 1‐hydroxyalkyltris(trimethylsilyl)silanes (Me3Si)3Si−C(OH)R1R2 (1a−f) isomerize by 1,2‐Me3Si/OH exchange to give the trimethylsilylmethylsilanols (Me3Si)2Si(OH)−C(SiMe3)R1R2 (4a−f) [R1,R2: a: Me, Me; b: H, 4‐MeC6H4; c: H, 4‐iPrC6H4; d: H, Mes; e: H, 2‐Me2NC6H4; f: H, 2,4,6‐(MeO)3C6H2]. A mechanism for the isomerization is proposed. In the case of the reaction of 1d with sulfuric acid, the silylsulfate (Me3Si)2Si(OSO3H)−C(SiMe3)HMes (5) was isolated. 5 is the intermediate in the H2SO4‐catalyzed isomerization of 1d and was converted in situ with methanol, acetic anhydride, HF or HCl to give the respective methoxysilane 6, acetoxysilane 7, fluorosilane 8, or chlorosilane 9. Deprotonation of 4a, d, f with sodium hydride causes a further rearrangement, a 1,3‐C,O‐trimethylsilyl migration, to give the siloxanes (Me3Si)2(Me3SiO)Si−CHR1R2 (11a, d, f).

Preparation and Synthetic Utility of 1-Trimethylsiloxyalkyl-bis(trimethylsilyl)silanes, (Me3Si)2SiH-C(OSiMe3)R1R2

“…The rearrangement of 5 into 10 is comparable with the acid promoted conversion of 1 into bis(trimethylsilyl)-1-trimethylsilylalkylsilanols, which we described recently [8]. In both cases the reaction is supposed to proceed through a carbenium ion transition state 8.…”

“…Similarly, 12 d and 12 g were also reluctand in a Cl/OSiMe 3 exchange and formation of 13 d or 13 g, resp., and their resultant products. Interestingly, also the above mentioned acid induced rearrangement of 1-hydroxyalkyl-tris(trimethylsilyl)silanes 1 into 1-trimethylsilylalkyl-bis(trimethylsilyl)silanols [8] could as well not be performed with the tertbutyl and the 2,6dichloroderivatives, resp. [11].…”

The Cationic Rearrangement of (3-Hydroxy-1-propenyl)tris(trimethylsilyl)silanes into (1-Trimethylsilyl-2-propenyl)bis(trimethylsilyl)silanols − Experimental and Theoretical Studies

“…Under the same conditions, however, 8b and 8c underwent rapid rearrangements and after aqueous workup of the reaction mixtures we obtained the silanols 13b and 13c, respectively. Sulfuric acid proved to be most effective for the acid-catalyzed isomerization of 1-hydroxyalkyl-tris(trimethylsilyl)silanes (1). [1] Thereforeand also because of the convenient experimental procedure -we used only this catalyst in all the studies described below.…”

“…Recently we found that 1-hydroxyalkyltris(trimethylsilyl)silanes (1) undergo a rapid isomerization in the presence of strong acids into 1-trimethylsilylalkylbis(trimethylsilyl)silanols (6) (Scheme 1). [1] The reaction path was interpreted in terms of a cationic rearrangement initiated by an acidcatalyzed elimination of water from the alcohol 1 and formation of the carbenium ion 2. The subsequent 1,2-Si,C migration of one trimethylsilyl group, and attack of X Ϫ , the conjugate base of the acid used as the catalyst, at the central silicon atom produces the intermediate 5, which after hydrolytic workup affords the silanol 6.…”

“…Chromatographic separation of the residue (silica gel, heptane/ethyl acetate 20:1) gave 0.14 g (26%) of the chlorosilane 12c and 0.15 g (30%) of the silanol 13c. 12c: Colorless oil 1. H NMR ([D 6 ]benzene): δ ϭ 0.18, 0.22 and 0.27 X-ray diffraction data were collected with a Bruker P4 four-circle diffractometer, Mo-Ka radiation, graphite monochromator, crystal size 0.48 ϫ 0.44 ϫ 0.41 mm 3 , T ϭ 293(2)K, C 25 H 42 OSi 4 , M ϭ 470.95, colorless prism, monoclinic, a ϭ 9.205(2), b ϭ 12.684(7), c ϭ 13.226(4) Å , β ϭ 94.78(3)°, V ϭ 1538.8(10) Å 3 , Z ϭ 2, space group Pn, ρ ber ϭ 1.016 Mg m Ϫ3 , µ ϭ 0.206 mm Ϫ1 , F(000) ϭ 512, data collection range: 4.46Յ 2Θ Յ 44.00, Ϫ9 Յ h Յ 9, Ϫ13 Յ k Յ 13, Ϫ13 Յ l Յ 13, 4054 reflections collected, 3776 independent and 3156 observed [I Ͼ 2σ (I)], R 1 ϭ 0.0452 (obs.…”