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43.8.2.6.4 Method 4: The Eschenmoser–Tanabe Fragmentation of Epoxy Ketones

DOI: 10.1055/sos-SD-043-00415

Krueger, A.Science of Synthesis, (200843537.

Instead of cyclopropyl compounds as substrates for coarctate reactions, it is also possible to use enones. After transformation into epoxy ketones and subsequent formation of the respective tosylhydrazone, the fragmentation yields an alkyne and a ketone (Scheme 75).[‌282‌‌287‌] Usually the reaction is carried out under acidic (preferred) or basic conditions at room temperature. Although the mechanism of this reaction is related to the rearrangement of cyclopropylcarbenes, the reaction conditions do not favor the formation of carbenes or diazo compounds.[‌263‌] Other mechanistic facts are responsible for the preferred reaction in systems fixed in an endo conformation (similar to the endo preference in cyclopropylcarbene rearrangements). Several examples of the EschenmoserTanabe reaction have been described in the literature. Many of them are cleavages of the A-ring of steroids (see Table 15).

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MeMMMM8 (8.88 eeeee), MM8Me8/MeMM (8:8), 88°M, 88e, eeee 88°M, 8e 88 [‌888‌]
MeMMMM8 (8.88 eeeee), MM8Me8/MeMM (8:8), 88°M, 88e, eeee 88°M, 8e 88 [‌888‌]
MeMMMM8 (8.88 eeeee), MM8Me8/MeMM (8:8), 88°M, 88e, eeee 88°M, 8e 88 [‌888‌]
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MeMMMM8, MM8Me8/MeMM (8:8), 88°M, 88e, eeee ee, 8e 88 [‌888‌]
MeMMMM8, MeMM, 888°M, 88eee, eeee 8°M, 88e, eeee MeMM8, ee, 8e 88 [‌888‌]
8,8-eeeeeeeeeeeeeeeeeeeeee, MMM, 88°M, 88eee, eeee 8°M, 88e, eeee eeeeeeee (8 eeeee), ee, 88eee 88 [‌888‌]
8,8-eeeeeeeeeeeeeeeeeeeeee, MMM, 88°M, 88eee, eeee Me8MM8, 88°M, 8e, eeee 88°M, 8e 88 [‌888‌]
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References