71092-50-7Relevant articles and documents
Tandem Transformations Involving Allylic Silanes. 2. Highly Diastereoselective Substitutions Involving [(Trialkylsilyl)methyl]cyclohexene Derivatives with Aldehydes. Synthetic Studies on the Problem of Lewis Acid-Promoted Protodesilylation and Enolization
Organ, Michael G.,Winkle, Derick D.,Huffmann, John
, p. 5254 - 5266 (2007/10/03)
Diels-Alder cycloaddition of 2-[(trialkylsilyl)methyl]-1,3-butadienes with a variety of dienophiles and substitution reactions between these allylsilane-containing adducts and aldehyde or acid chloride electrophiles have been combined into "tandem sequential reactions." These tandem sequences proceed with equal or greater yield (50-80%) than the reactions performed separately with no decrease in regio- or stereoselectivity. The sequence produces cyclic compounds with three or four stereogenic centers with good to excellent diastereoselectivity from three simple, noncyclic, and achiral reaction partners. Unprecedented levels of diastereoselectivity (de >93%) have been achieved in allylic substitution reactions involving substituted [(trialkylsilyl)methyl]cyclohexene derivatives with aldehyde electrophiles. During the course of these studies, protodesilylation of allylsilanes has been investigated in detail, and a cocatalyst system of TiCl4 and Me2AlCl has been developed that has eliminated silicon loss in the substitution reactions studied. Lewis acid-promoted enolization of ester and ketone substrates with chiral centers adjacent to the carbonyl moiety has been studied also. It has been shown that this event in our studies occurs primarily during catalyst quench. This isomerization is prevented by quenching the catalyst with a Lewis base, such as methanol or triethylamine, prior to aqueous workup.
Solvolyses of 3-Oxo- and 3-Methylenebicyclooct-1-yl Triflates: Through-Bond Interaction of a β-Carbonyl Lone Pair with a Cationic p Orbital
Yoshida, Masayasu,Takeuchi, Ken'ichi
, p. 2566 - 2572 (2007/10/02)
The rates of solvolysis of 3,3-dimethyl-2-oxobicyclooct-1-yl triflate (1b), 2-methylenebicyclooct-1-yl triflate (2b), 5,5-dimethyl-3-oxobicyclooct-1-yl triflate (3b), 3-oxobicyclo-oct-1-yl triflate (4b), 3-methylenebicyclooct-1-yl triflate (5b), 3,3-dimethylbicyclooct-1-yl triflate (6b), and bicyclooct-1-yl triflate (7b) have been determined in 80percent ethanol at 25 deg C.The 18O- and deuterium-labeling studies exclude both carbonyl addition and the enolization processes in the solvolyses of 3b and 4b.The rate ratios 1b/6b and 2b/7b are 10-9.1 and 10-3.9, respectively, indicating that the oxo substituent at the C(2) position is more electron withdrawing than the methylene substituent at the same position.In contrast, the rate ratios 3b/6b and 5b/7b, 10-2.3 and 10-2.2, respectively, are comparable with each other.Moreover, the rate ratio 4b/5b is 2.3, suggesting that the 3-oxo substituent is less electron withdrawing than the 3-methylene substituent with respect to the cationic center.Evaluation of the inductive effect of the oxo substituent at the C(3) position by means of the reported rates of solvolysis of various 2- or 3-substituted and unsubstituted bicyclooct-1-yl p-nitrobenzenesulfonates (14, 13, and 15, respectively) indicates a rate enhancement of 103-104 for 3b and 4b.This marked enhancement is interpreted as evidence of the stabilization of the 3-oxo carbocation by a through-bond interaction between the β-carbonyl lone pair and the cationic p orbital.The mY relationships and the formation of fragmentation products 11 (9percent) and 12 (20percent) in the methanolyses of 3-oxo compounds 3b and 4b, respectively, support the through-bond interaction.
