Journal of Organic Chemistry p. 395 - 405 (1980)
Update date:2022-08-05
Topics:
Jacobson, Richard M.
Lahm, George P.
Clader, John W.
The trimethylsilyl- (2) and ethoxyethyl- (4) protected cyanohydrins of α,β-unsaturated aldehydes are utilized as three-carbon annelation reagents.Metalated reagent 2 displays exclusive α reactivity with aldehydes and ketones at -78 deg C.Metalated reagent 4 displays exclusive α reactivity at -78 deg C and exclusive γ reactivity at 0 deg C.Reagent 4 thus allows for complete regiocontrol in its addition to aldehydes and ketones which permits selective addition of either a homoenolate or an acyl anion equivalent.Metalation of the α product 11 at -78 deg C with subsequent warming to 0 deg C produces exclusively the γ product, confirming the reversible nature of the addition to the carbonyl.The derived α '-trimethylsiloxy enones 17 (R3=Me3Si), α '-hydroxy enones 17 (R3=H), α '-acetoxyenones 17 (R3=Ac), and γ-lactones 10 are useful cyclopentenone precursors.Treatment of 17 with p-TsOH in toluene at reflux produces cyclopentenones.The reaction proceeds via the postulated intermediacy of a pentadienyl cation 15 which undergoes in situ electrocyclic ring closure.
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