87143-45-1Relevant academic research and scientific papers
Metallated Nitrogen Derivatives of Carbonic Acid in Organic Synthesis, XXVII. - Homoaldol Reaction, VII. Lithiation of Acyclic 2-Alkenyl N,N-Dialkylcarbamates. - Silylation and γ-Selective α-Hydroxyalkylation of Homoenolate Reagents
Hoppe, Dieter,Hanko, Rudolf,Broenneke, Alfons,Lichtenberg, Florian,Huelsen, Ede van
, p. 2822 - 2851 (2007/10/02)
2-Alkenyl N,N-dialkylcarbamates 20 are deprotonated by n-butyllithium/TMEDA to form lithium compounds 21 which are versatile homoenolate reagents.The diisopropylcarbamoyl group is not attacked by butyllithium below -70 deg C.Due to the high kinetic acidity of the α-protons in 20, 1-oxyallyl anions 21, bearing up to two alkyl groups in any given distribution are accessible. - The reaction of 21 with chlorotrimethylsilane gives silanes 28 and/or 29.The regiochemistry of the silylation is mainly controlled by the position of methyl groups present in 21. - The addition of aldehydes or ketones 14 to 21 proceeds with high γ-selectivity yielding 4-hydroxyenol carbamates 30, which are methanolized in the presence of catalytic amounts of mercuric salts to afford 2-methoxytetrahydrofuranes (γ-lactol ethers) 33.Subsequent oxidation of 33 yields γ-lactones 34.Alternatively, O-acetyl derivatives 32 are hydrolyzed to afford γ-acetoxyalkanals or -alkanones 36.Alltogether, the method provides a general and flexible way for realization of homoaldol reactions. - (2E)- and (2Z)-butenyllithium compounds 21g and h are configuratively stable at the reaction conditions, which is an important requirement for accomplishment of syn- and anti-diastereoselective homoaldol reactions. - S-(2-alkenyl) N,N-dimethylthiocarbamates 12 are similarly deprotonated and hydroxyalkylated, but hydrolysis of enol thiocarbamates 15 to prepare homoaldols is not feasible.
HIGHLY DIASTEREOSELECTIVE SYNTHESIS OF DI-AND TRISUBSTITUTED 4-BUTANOLIDES FROM ALDEHYDES AND KETONES VIA THREE-CARBON-EXTENSION BY ALLYLIC HOMOENOLATE REAGENTS
Hoppe, Dieter,Broenneke, Alfons
, p. 1687 - 1690 (2007/10/02)
Lithiated or titanated O-allyl carbamates 7 or 8 add to aldehydes and ketones regio- and diastereoselectively to yield-O-(4-hydroxy-1-alkenyl)carbamates 9, which are converted to γ-lactones 12 with an one-pot procedure.
