Intramolecular Michael like process

Jung and coworkers reported AlBr3/Me3Al system as an effective mixed Lewis acid system for Diels-Alder reaction of sterically hindered dienophiles and dienes (Scheme 6.126) [150]. It was proposed that this reaction proceeds via Mukaiyama-Michael addition of silyl enol ether moiety to cyclohexenone followed by intramolecular Michael like process. 

Very likely the ammonium fluorides are the proton sources and therefore the reason for incomplete conversions, since potassium fluoride in acetonitrile gives high yields in a very elegant [3 + 2]-annuIation process 87). It combines a Michael addition to a vinyl phosphonium salt with an intramolecular Wittig reaction and proceeds only in the presence of 18-crown-6 with satisfying yield. This cyclopentene synthesis has been executed in a repetitive manner to prepare linear triquinanes as illustrated in Scheme 6. Unfortunately, the sequence is non-stereoselective with regard to the ethoxycarbonyl functions. 

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