207925-79-9Relevant academic research and scientific papers
[3 + 4] Annulation of α,β-unsaturated acylsilanes with enolates of α,β-unsaturated methyl ketones: Scope and mechanism
Takeda, Kei,Nakajima, Akemi,Takeda, Mika,Okamoto, Yasushi,Sato, Taku,Yoshii, Eiichi,Koizumi, Toru,Shiro, Motoo
, p. 4947 - 4959 (2007/10/03)
Reactions of the E and Z isomers of (β-(trimethylsilyl)acryloyl)(tert- butyl)dimethylsilanes with lithium enolate of α,β-unsaturated methyl ketones at -80 to -30 °C afford cis-5,6- and trans-5,6-disubstituted 3- cyclohepetenones, respectively. The same [3 + 4] annulation is observed in the reaction of (β-(tri-n-butylstannyl)acryloyl)silanes. The annulation products are readily transformed into 4-cycloheptene-1,3-dione by treatment with NBS or mCPBA. The observed sterospecificity in the annulation is explained by the reaction pathway that involves an anionic oxy-Cope rearrangement of 1,2-divinylcyclopropanediol intermediate generated via Brook rearrangement of the 1,2-adduct of a lithium enolate. Isolation of vinylcyclopropanol derivative from the reaction of (β-(tri-n- butylstannyl)acryloyl)silanes with lithium enolate of 2'-bromoacetophenone and its transformation into cycloheptenone derivative with LDA provide strong support for the proposed mechanism. Further support is obtained from the reactions of 1,2-divinylcyclopropyl acetates with 2 equiv of MeLi affording cycloheptenones stereospecifically. Also, β-alkyl-substituted acryloylsilanes and cycloalkenylcarbonysilanes are found to participate in the [3 + 4] annulation.
