RESUMEN
The asymmetric Reppe carbonylation reactions provide a straightforward access to α-chiral carbonyl compounds. The reported paradigms predominantly adopted precious palladium as the catalyst. Here we report a nickel-catalyzed asymmetric carbonylation of cyclopropenes with phenyl formate and CO/ROH, respectively. This asymmetrical synthetic protocol features high atom economy, good functional group tolerance, which rapidly constructs polysubstituted cyclopropanecarboxylic derivatives with excellent diastereo- and enantioselectivity. The synthetic utility is demonstrated by facile conversion of the chiral products into bioactive molecules such as (-)-Tranylcypromine and (-)-Lemborexant.
RESUMEN
The diastereoselective double carbometalation reaction of cyclopropenes provides, in a single-pot operation, two ω-ene-[1,1]-bicyclopropyl ester derivatives. One regioisomer then undergoes a Pd-catalyzed addition of aryl iodide to provide skipped dienes possessing several distant stereocenters including two congested quaternary carbon centers with excellent diastereoselectivity.
RESUMEN
The chiral enantiopure cobalt(III) complex Δ-[Co((S,S)-dpen)3 ]3+ 2Cl- B(C6 F5 )4 - (Δ-(S,S)-23+ 2Cl- B(C6 F5 )4 - ; dpen=1,2-diphenylethylenediamine) is an effective catalyst, together with pyridine (10â mol % each), for enantioselective additions of substituted cyanoacetate esters NCCH(R)CO2 R' to acetylenic esters R''C≡CCO2 R'''. In the resulting adducts NC(R'O2 C)C(R)CR''C=CHCO2 R''', C=C isomers in which the CO2 R''' moiety is trans to the new carbon-carbon bond dominate (avg. ratio 98:2). These are obtained in 70-98 % ee (avg. 86 %; data for optimum R' and R'''), as determined by 1 Hâ NMR with the chiral solvating agent Λ-(S,S)-23+ 2I- B(3,5-C6 H3 (CF3 )2 )4 - . NMR experiments show that the cyanoacetate and acetylenic esters and pyridine can hydrogen bond to certain NH groups of the catalyst. Rates are zero order in the cyanoacetate and acetylenic esters as well as the catalyst, and implications are discussed.
RESUMEN
The application of stereochemically defined acyclic fully substituted enolates of ketones to the enantioselective synthesis of quaternary carbon stereocenters would be highly valuable. Herein, we describe an approach leading to the formation of several new stereogenic centers through a combined metalation-addition of a carbonyl-carbamoyl transfer to reveal inâ situ stereodefined α,α-disubstituted enolates of ketone as a single stereoisomer. This approach could produce a series of aldol and Mannich products from enol carbamate with excellent diastereomeric ratios.
RESUMEN
The regio- and stereoselective formation of stereodefined polysubstituted silyl ketene aminals is easily achieved through selective combined carbometalation-oxidation-silylation reactions. These substrates are ideal candidates for Mukaiyama aldol reactions with aliphatic aldehydes as they give the aldol products with a quaternary carbon stereocenter α to the carbonyl groups in outstanding diastereoselectivities.