Cross-aldol reactions of levoglucosenone and its derivatives with cyclohex-1-en-1-ol ethers
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The reaction of levoglucosenone with cyclohex-1-en-1-yl trimethylsilyl ether under Mukaiyama reaction conditions gave [1 + 2]-Michael–aldol condensation product with participation of the acetal center. The reaction was accompanied by opening of the 1,6-anhydro bridge and intramolecular hemiketalization by the hydroxy group of the 2-oxocyclohex-1-enyl fragment. Under analogous conditions, dihydrolevoglucosenone gave rise to four diastereoisomeric 1,2-addition products. Internal cyclohex-1-en-1-ol ether obtained by treatment of the Michael adduct of levoglucosenone and cyclohexanone with Ac2O–ZnCl2 underwent intramolecular Mukaiyama reaction involving substituted α-carbon atom of the cyclohexanone fragment and acetal moiety to afford spiro derivative and product of subsequent AdE1 acetylation of intermediate α′-cyclohexenyl ether fragment.
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