[17082-61-0] · C10H22O2Si2 · 1,2-Bis(trimethylsilyloxy)cyclobutene · (MW 230.45)
Physical Data: bp 88-92 °C/13-14 mmHg; d 0.89 g cm-3.
Solubility: sol hydrocarbons and ethers.
Form Supplied in: not commercially available.
Preparative Methods: prepared as a colorless liquid by acyloin condensation of Diethyl Succinate (dispersed Na in toluene or Et2O, reflux) using Chlorotrimethylsilane as trapping agent.4 An Organic Synthesis preparation is available.4c
Handling, Storage, and Precautions: use in a fume hood; the compound is stable for years if stored in a tightly screw-capped bottle. Prolonged exposure to moist air leads to decomposition.
1,2-Bis(trimethylsilyloxy)cyclobutene (1) reacts in an aldol-type reaction with aldehydes and acetals in the presence of Boron Trifluoride Etherate. The adducts are easily converted into 2- or 2,2-substituted 1,3-cyclopentanediones in high yields via a pinacol rearrangement (eq 1). Acetals of cyclic ketones lead to spiro[4.n] ring systems.1,5a This two-step geminal acylation provides an efficient and general annulation procedure which can be carried out in a one-pot process. Cyclic acetals (dioxolanes, dioxanes), in the presence of a large excess of BF3.OEt2, provide a superior yield of the cyclopentanediones.6 With Tetra-n-butylammonium Fluoride catalysis the reactions stop at the butanone stage.7 Starting from thioacetals, the rearrangement can be carried out under mild, neutral conditions (Mercury(II) Chloride).8
o-Alkynyl acetals react with (1) directly to give polycyclic unsaturated ketones (eq 2); a different pathway is observed for a terminal alkyne (eq 3).9
Differently functionalized cyclopentenones, b-hydroxy-cyclopentanone, or b-alkylidenecyclopentanones are obtained when the butanone is modified prior to the rearrangement.1,5d The spiroannulation is stereoselective because of equatorial preference of the aldol-type reactions and complete inversion during the pinacol rearrangement (eq 4).
In the presence of Tin(IV) Chloride, (1) and an acetal undergo two successive reactions, involving ring cleavage of the aldol adduct (eq 5).3,5g Reaction of the enol silyl ether with carbon or sulfur electrophiles leads to 5-substituted 4-keto esters.1,3 Also 5-alkoxy-1,4-diketones can be obtained.3,10
Photochemical cycloaddition of (1) to 2-cyclopentenones and 2-cyclohexanones (except 2-alkyl-2-cyclohexenones) leads to tricyclo[4.3.0.02,6]nonane-2-ones and tricyclo[4.4.0.02,7]decane-2-ones, respectively.2 With 5-alkyl-2-cyclohexenones the addition occurs trans to the 5-substituent (eq 6).11 Subsequent to manipulation (reduction, organometallic, or Wittig reaction) of the keto function in the adduct, oxidative a-diol cleavage provides a facile entry into bicyclo[4.3.0]nona-2,5-diones and bicyclo[4.4.0]deca-2,5-diones.2,11,12 The respective cis-hydrindanes and cis-decalanes, such as (2), are functionalized at three positions vicinal to the ring junction.
Reagent (1) can be transformed into 1,2-cyclobutanedione, cis-1,2-cyclobutanediol, 2-aminobutanone, and 2-t-alkyl-2-hydroxybutanone.13 b-C-Glycosides are available upon Titanium(IV) Chloride-mediated reaction of (1) with glycosyl acetates.14
This is obtained upon thermolysis (180 °C, 84%) of (1) and can be used in Diels-Alder reactions with alkynic esters.15
University of Gent, Belgium