Comparison of the electronic effect and the steric influence between the 1,1,2,2,2-pentamethyldisilanyl and the trimethylsilyl groups
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 produc...
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Published in | Journal of organometallic chemistry Vol. 453; no. 1; pp. 21 - 28 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
Lausanne
Elsevier B.V
29.06.1993
Elsevier Science |
Subjects | |
Online Access | Get full text |
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Summary: | 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. |
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ISSN: | 0022-328X 1872-8561 |
DOI: | 10.1016/0022-328X(93)80322-3 |