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8716315 
Journal Article 
Diastereoselective addition of γ-substituted allylic nucleophiles to ketones: Highly stereoselective synthesis of tertiary homoallylic alcohols using an allylic tributylstannane/stannous chloride system 
Yasuda, M; Hirata, K; Nishino, M; Yamamoto, A; Baba, A 
2002 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
124 
45 
13442-13447 
English 
12418896 
The diastereoselective addition of γ-substituted allylic nucleophiles to ketones has been accomplished to give tertiary homoallylic alcohols. The reaction of tributylcinnamyltin 1a with simple ketones 2 in the presence of stannous chloride (SnCl2) gave the tertiary homoallylic alcohols 3, which include the anti form (based on Ph and OH), with high diastereoselectivity. In the reaction course, transmetalation of tributylcinnamyltin 1a with SnCl2 proceeds to form an active nucleophile which is tentatively considered to be a cinnamyltin(II) species. A cyclic transition state A is favorable because the chlorinated tin(II) center is highly capable of accepting ligands. The other diastereomers (syn form) 4 were obtained in the reaction of tributylcinnamyltin 1a with ketones 2 by the use of BF3·OEt2 instead of SnCl2. This reaction proceeds through an acyclic transition state in which BF3 acts as a Lewis acid for activation of ketones. When 3-tributylstan-nylcyclohexene 1b or 3-tributylstannylcyclopentene 1c was used with SnCl2, high diastereoselective formation of the corresponding homoallylic alcohols 6 which have the syn form (based on ring chain and OH) was observed. The selectivity was also explained by the cyclic transition state B. When tributylcrotyltin 1d or 1e was used, the stereochemistry of the products depends on the additives (SnCl2 or BF3·OEt2), substituents of ketones, and reaction temperature. It is interesting that those additives compensate for each other in terms of diastereoselective alkylation. The alkylation of α-alkoxy, aryloxy, or hydroxyketones 16 was achieved in extremely high selectivity using an allylic tributyltin 1a-c/SnCl2 system. The chelation by carbonyl and β-oxygens provides a rigid transition state (E or F) for selective reactions. It is noted that the hydroxyketone can be used without protection in this reaction system. The relative stereochemistry of the produced tertiary homoallylic alcohols was determined on the basis of x-ray analyses.