Highly Stereoselective Synthesis of Bicyclo[n.3.0]alkanes by Titanium Tetrachloride Promoted [3 + 2] Cycloaddition of Allylsilanes and 1-Acetylcycloalkenes
摘要:
AbstractThe titanium tetrachloride promoted reaction of allylsilanes 1 with 1‐acetylcyclohexene is shown to afford the silylbicyclo[4.3.0]nonanes 9 ([3 + 2] cycloaddition products) along with the 1‐acetyl‐2‐allylcyclohexane 4 (Hosomi‐Sakurai product). Here we report that systematic variation of the substituents at the silicon atom of 1 allows suppression of the classical Hosomi‐Sakurai reaction in favor of the [3 + 2] cycloaddition. Cycloaddition of the allylsilanes 1d, 1i, and 1 k with 1‐acetylcycloalkenes 10, containing a 5‐, 6‐, 7‐, 8‐, or 12‐membered ring, gives rise to the corresponding silylbicyclo[n.3.0]alkanes 11 – 13. The cycloaddition of allyltriisopropylsilane (1 k) and 1‐acetyl‐2‐methylcycloalkenes 15 provides silylbicyclo[n.3.0]alkanes 16 with two contiguous quaternary carbon centers. The stereochemistry of the silylbicyclo[n.3.0]alkanes 11 a ‐ c and 14 is unambiguously determined by X‐ray analysis and 13C NMR spectroscopy.
Diallylsilanes can be made to rearrange upon treatment with I2. Of the silanes tested, diallyldiphenylsilane showed the greatest propensity to undergo this intramolecular carbocation allylation process. After etherification of the initially formed iodosilane, the products from this transformation represent useful synthetic intermediates, suitable for alkylation and cross-metathesis/annulation reactions
regio- and diastereoselective cyclization/hydroarylation reaction of 1,5- and 1,6-dienes with aromatic ethers and tertiary anilines was established by a cationic 2-picoline-tethered-half-sandwich scandium alkyl catalyst, which constitutes a process for producing a diverse array of cis-1,3-disubstituted arylated and trans-1,2-disubstituted benzylated methylcyclopentanederivatives in one step with 100% atom-efficiency