Palladium-catalyzed asymmetric addition of pronucleophiles to allenes.
Simple additions are the most atom economic way to effect alkylations. The ability to effect the hydrocarbonation of allenes asymmetrically then becomes a highly efficient alkylation protocol. The first example of such a protocol involves the ability of a palladium(0) catalyst derived from palladium trifluoroacetate dimer and the bis-2-diphenylphosphinobenzamide of trans-1,2-diamininocyclohexane to catalyze additions to benzyloxyalkene. Various substituted Meldrum's acids including hydroxy Meldrum's acid react well in the presence of 1 mol % trifluoroacetic acid to give one regioisomer with ee's ranging from 82 to 99%. Switching to azlactones to access unusual quarternary amino acids requires somewhat more basic conditions. Thus, use of 2 mol % potassium alpha-butoxide and 20 mol % hippuric acid leads to a smooth reaction to produce a simple regiosomer. This nucleophile raises the question of facial selectivity with respect to both the nucleophile and the electrophile. Excellent diastereoselectivity (dr 13-20:1) and enantioselectivity (85-94% ee) are obtained. Thus, a new approach for asymmetric allylic alkylations of carbon pronucleophiles by simple additions provides a very efficient, more atom economic strategy for asymmetric C-C bond formation.
Trost
Barry M
BM
Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA. bmtrost@stanford.edu
Jäkel
Christoph
C
Plietker
Bernd
B
D000466:Alkadienes / Q000737:chemistry*; D000478:Alkylation; D001372:Aza Compounds / Q000737:chemistry; D002384:Catalysis; D004146:Dioxanes / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry; D010165:Palladium / Q000737:chemistry*
D000466:Alkadienes; D001372:Aza Compounds; D004146:Dioxanes; D007783:Lactones; D009942:Organometallic Compounds; C025947:propadiene; D010165:Palladium; C076489:Meldrum's acid