Cyclopentenyllithium Additions to Chiral Aldehydes. Diastereofacial Selectivity Indicating the Absence of a Pronounced Neighboring Carboxylate Anion Effect
The 1,2-addition of cyclopentenyllithium to a series of three five-membered aldehydo esters and their hemiacylals has been examined in order to assess the level and direction of facial selectivity surrounding nucleophilic attack at the aldehyde carbonyl and to clarify possible electronic and steric contributions stemming from neighboring functional groups.Neither methyl substitution of the acetic acid (ester) side chain nor the interchange of ester for carboxylate anion serve as important diastereocontrol elements.Instead, diastereofacial selectivity in these and related cyclic carboxyaldehydes is governed by the inherent structural features of the ring system to which the functional group is attached.The convinient preparation of a complete subset of isomerically pure bicyclic lactones carrying five stereogenic centers is reported.
Friedrich, Dirk,Paquette, Leo A.
p. 3831 - 3840
(2007/10/02)
THE SELECTIVE CLAISEN AND DIECKMANN ESTER CONDENSATION PROMOTED BY DICHLOROBIS(TRIFLUOROMETHANESULFONATO)TITANIUM(IV)
Inter and intramolecular condensations (the Claisen and the Dieckmann condensations) between ester functions have been performed by the combined use of dichlorobis(trifluoromethanesulfonato)titanium(IV) (=dichlorobis(triflato)titanium(IV)) and tertiary amine under mild reaction conditions.These results led to the development of the selective (crossed) Claisen and Dieckmann ester condensation between methoxymethyl ester and methyl ester, in that, dichlorobis(triflato)titanum(IV) contribute to control the direction of the reaction.
Tanabe, Yoo
p. 1917 - 1924
(2007/10/02)
DICHLORO-BIS(TRIFLUOROMETHANESULFONATO)TITANIUM(IV) AS AN EFFECTIVE PROMOTER IN THE CLAISEN ESTER CONDENSATION
Inter- and intra-molecular condensation (the Claisen and the Dieckmann condensations) between ester functions have been effected by the combined use of dichloro-bis(trifluoromethanesulfonato)titanium(IV) and tertiary amine under mild conditions.
Tanabe, Yoo,Mukaiyama, Teruaki
p. 1867 - 1870
(2007/10/02)
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