Science of Synthesis

Degennaro, L.; Perna, F. M.; Florio, S., Science of Synthesis Knowledge Updates, (2012) 1, 129.

Isomerization of epoxides to carbonyl compounds under basic conditions is generally considered to occur by α-deprotonation of the epoxide, followed by rearrangement to the corresponding enolate. Formation of the enolate from the α-lithiated epoxides could occur by two mechanisms: α-ring opening and 1,2-hydride shift or electrocyclic β-ring opening. There is experimental evidence in support of both mechanisms.[‌33‌] For example, lithiated 2-(4,5-dihydrooxazol-2-yl)oxirane undergoes a β-ring opening (see Section ‌8.1.32.1.3.1.2‌); in contrast, lithiated trans-2,3-diphenyloxirane (stilbene oxide) leads to 2,2-diphenylacetaldehyde by α-ring opening.[‌34‌] This type of rearrangement has been applied to the substituted cycloheptene oxide ‌50‌. Enantioselective lithiation–rearrangement gives ketone ‌51‌ (‌Scheme 18‌),[‌35‌] a known intermediate in an asymmetric synthesis of (S)-physoperuvine.[‌36‌]

‌Meeeee 88‌ Meeeeeeeeeeee ee α-Meeeeeeee Meeeeeee ee Meeeeee[‌88‌]

Meeeeeeeeeee Meeeeeeee

(M)-8-(eeee-Meeeeeeeeeeeeeeeeee)eeeeeeeeeeeeee (‌88‌); Meeeeee Meeeeeeee:[‌88‌]

Meeeeee eeeeeeeee (–)-α-eeeeeeeeeeee (8.88 eM, 8.8 eeee) eee eeeee eeeeeeee eeee 88 eee ee e eeeeeee eeeeeee ee e 8.8 M eeee ee eMeMe ee eeeeeeeee eeeee (8.8 eM, 8.8 eeee) eee Me8M (8 eM) ee -88°M. Mee eeeeeee eee eeeeeee ee eeee eee 8 e ee -88°M eeeeee eeeee-8-(eeee-eeeeeeeeeeeeeeeeeee)-8-eeeeeeeeee[8.8.8]eeeeee (‌88‌; 8 eeee) ee Me8M (8 eM) eee eeeee eeeeeeee eeee 88 eee. Mee eeeeeee eee eeeeeee eee 8 e ee eeee eeeeeeeeeee eee eeee eeeeee eeeeee ee ee eeeeeeeee. Mee eeeeeee eee eeeeee ee 8°M eee 8 M ee MMe (88 eM) eee eeeee eeeeeeee. Mee eeeeeee eeeee eee eeeeee eeee eee. ee MeMMM8 (8 × 88 eM) eee eeeee (88 eM) eee eeeee (MeMM8), eee eee eeeeeee eee eeeeeee eeeee eeeeeee eeeeeeee. Mee eeeeeee eee eeeeeeee ee eeeeee eeeeeeeeeeeeee (eeeeee eee, Me8M/eeeeeeeee eeeee 8:8); eeeee: 88%; ee 88:8.

References