Comparison of the electronic effect and the steric influence between the 1,1,2,2,2-pentamethyldisilanyl and the trimethylsilyl groups

• Published in: Journal of organometallic chemistry Vol. 453; no. 1; pp. 21 - 28
• Main Authors: Hwu, Jih Ru, Wetzel, John M., Lee, John S., Butcher, Raymond J.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 29.06.1993; Elsevier Science
• Subjects: Alicyclic compounds; Alicyclic compounds, terpenoids, prostaglandins, steroids; Chemistry; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Heterocyclic compounds; Organic chemistry; Organic compounds; Physics; Preparations and properties; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Lewis acid; Substituent effect; Chemical rearrangement; Silicon Organic compounds; Saturated compound; Organic silane; Acid catalysis; Aldehyde; Tricyclic compound; Oxygen heterocycle; Spiran; Dienone; Bicyclic compound; Epoxidation; Secondary alcohol; Homoallylic compound; Monocyclic compound
• ISSN: 0022-328X; 1872-8561
• DOI: 10.1016/0022-328X(93)80322-3

A comparison of the electronic effects expressed by the Me 3SiMe 2Si-; and Me 3Si- groups towards carbocationic intermediates was made by study of acid-catalyzed rearrangements of decalin epoxides 3 and 4. Reaction of the Me 3SiMe 2Si-epoxide 3 with BF 3 · Et 2O in CH 2Cl 2 at -50°C gave four products: B-ring contracted spirocyclic alcohol 9 (21%), methyl-migrated decanol 12 (23%), A-ring contracted aldehyde 15 (21%), and fluorohydrin 17 (14%). Under the same conditions, Me 3Si-epoxide 4 afforded alcohol 9 (24%), decanol 12 (18%), aldehyde 16 (23%; cf. 15), and fluorohydrin 18 (13%; cf. 17). These results show that the Me 3SiMe 2Si- and Me 3Si- groups exerted electronic influence to the same extents on carbocations. In HMPA and THF at -78°C, reagent Me 3SiMe 2SiLi reacted with cross-conjugated dienone 19 in a 1,4 fashion from the less hindered side to give enone 20 (63%) as the only adduct. In comparison with Me 3SiLi, reagent Me 3SiMe 2SiLi possessed better stereoselectivity. In addition, the Me 3SiMe 2Si- moiety with α configuration in 24 was able to prevent m-chloroperbenzoic acid ( m-CPBA) from attacking from the same face during epoxidation, such that β-epoxide 3 was obtained in 59% yield exclusively.