Asymmetric Synthesis of Highly Substituted ?-Lactones by Nucleophile-Catalyzed [2+2] Cycloadditions of Disubstituted Ketenes with Aldehydes (original) (raw)

I. General THF was purified by passing it through a neutral alumina column. Zinc metal (Strem) was activated with hydrochloric acid. Benzaldehyde (Aldrich), ptrifluoromethylbenzaldehyde (Aldrich), p-tolualdehyde (Aldrich), and 2-bromo-2methylpropanoylbromide (Aldrich) were distilled prior to use. Quinidine (Avocado), LiClO 4 (Alfa Aesar), 2-napthaldehyde (Aldrich), 4-acetylbenzaldehyde (Aldrich), DIBAL-H (1.0 M in THF; Aldrich), sodium azide (Alfa Aesar), DMSO (Aldrich), and npropylamine (Aldrich) were used as received. Non-commercially available αbromoacid bromides were synthesized according to a literature procedure. 1 Catalysts 1, 2 2, 3 and O-TMS-quinidine 4 were prepared as previously reported. All reactions were carried out under an atmosphere of nitrogen or argon in ovendried glassware with magnetic stirring, unless otherwise indicated.