(2＋2) Cycloaddition Reaction of Alkyl Enol Ethers with Acrylates by in Situ Generated Silyl Triflic Imide Catalyst

• Published in: Chemical & Pharmaceutical Bulletin Vol. 56; no. 8; pp. 1205 - 1206
• Main Authors: Kiyosei TAKASUa, b, Yuta MIYAKAWAb, Masataka IHARAb, c, Hidetoshi TOKUYAMAb
• Format: Journal Article
• Language: Japanese
• Published: Pharmaceutical Society of Japan 2008
• ISSN: 0009-2363

We describe here (2＋2) cycloaddition reaction of alkyl enol ethers with acrylates catalyzed by triethylsilyl triflic imide (Et3SiNTf2), which was in situ generated from triethylsilane and triflic imide. The reaction efficiently provides substituted cyclobutanes bearing alkoxy function in a stereosetective manner. Although cyclobutane ring is one of the fundamental carbocyclic skeletons, only a limited number of synthetic methods exists for the synthesis.1-3) As one of the solutions, we have reported (2＋2) cycloaddition reaction of silyl enol ethers with α,β-unsaturated esters catalyzed by EtAlCl2 (ca. 20 mol％ catalyst loading) to produce substituted cyclobutanes bearing siloxy moiety with high stereoselectivity.4-6) Recently, Corey's group developed its asymmetric variant giving enantiomerically enriched cyclobutanes using a chiral oxazaborolidine-AlBr3 catalyst.7) In the course of our continuous study directed to develop the practical process, we have found trifluoromethenesulfonimide (Tf2NH) efficiently catalyses the (2＋2) cycloaddition reaction.8,9)