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2004
Pyridine derivatives
R 0380
Investigations of α-Siloxy—Epoxide Ring Expansions Forming 1-Azaspirocyclic
— Cyclopentanol silyl ethers (I) and (III) undergo ring expansion in the pres51- 112 Ketones.
ence of TiCl4 exclusively in a 1,2-anti fashion. Cyclobutanol silyl ethers expand via either a 1,2-anti or 1,2-syn manner, depending on the Lewis acid promoter or the nature
of the silyl ether. A new method to obtain 3-substituted spiro compounds (XII), which
are not accessible from the above siloxy—epoxide substrates, is presented. It involves
the ring expansion of acid-labile epoxides (XI) under treatment with HCl. In addition,
carbocyclic spiro analogue (XIV) is also prepared as exclusive diastereomer. —
(DAKE*, G. R.; FENSTER, M. D. B.; FLEURY, M.; PATRICK, B. O.; J. Org. Chem.
69 (2004) 17, 5676-5683; Dep. Chem., Univ. British Columbia, Vancouver, B. C. V6T
1Z1, Can.; Eng.) — Klein
2004
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