2-tert-Butoxy-3-phenylcyclopropanone acetal, a stable precursor of lithiated 2-phenylcyclopropenone acetal

2-tert-Butoxy-3-phenylcyclopropanone acetal 8 was found to be a stable precursor of lithiated cyclopropenone acetal. Acetal 8 was used in the practical synthesis of cysteine proteinase inhibitors; isolated yield of the key intermediate 14 was better than the one by the previous method.