C<inf>2</inf>-symmetric enantiopure bis-α,β-butenolides as diastereoselective substrates in ethylene photocycloaddition

Several C2-symmetric bis-α,β-butenolides have been synthesised starting from D-mannitol. Their [2+2]-photocycloaddition to ethylene has been studied as a model reaction to evaluate the influence of the protecting groups of the central diol system on the facial diastereoselectivity. The trimethylsilyl derivative shows the highest selectivity. The bis-cyclobutane containing products have been converted into the enantiopure adducts of γ- hydroxymethyl-α,β-butenolide and ethylene.