PMID- 12889940
OWN - NLM
STAT- MEDLINE
DCOM- 20030929
LR  - 20080117
IS  - 0002-7863 (Print)
IS  - 0002-7863 (Linking)
VI  - 125
IP  - 31
DP  - 2003 Aug 6
TI  - Unusual effects in the pd-catalyzed asymmetric allylic alkylations: synthesis of 
      chiral chromans.
PG  - 9276-7
AB  - An examination of earlier reports of poor-to-modest results using Pd-catalyzed 
      asymmetric allylic alkylations (AAA) to effect cyclization to form 
      tetrasubstituted carbons reveals several novel factors that can influence this 
      class of reactions. Thus, carboxylate has a major effect on such cyclizations 
      wherein the ee increases from 14% ee favoring the S with no carboxylate to 84% ee 
      favoring the R enantiomer in the presence of 1 equiv of carboxylate. Changing the 
      double bond geometry from E to Z further increases the ee to 97%. Furthermore, 
      the chiral catalyst that forms the R enantiomer with the E-alkene forms the S 
      enantiomer with the Z alkene. In contrast to trisubstituted alkene substrates, 
      disubstituted ones show a decrease in ee in going from the E to Z alkenes. The 
      role of carboxylate appears to be a ligand to Pd during the catalytic cycle, a 
      previously unsuspected phenomenon since such reactions are generally believed to 
      involve pi-allylpalladium cationic complexes. The dependence upon alkene geometry 
      helps define the nature of the chiral pocket which better accommodates a Z alkene 
      compared to an E alkene. The results are compatible with the 
      enantiodiscriminating step being ionization which occurs by coordination of the 
      palladium to one of the two prochiral faces of the double bond. A synthesis of 
      (+)-clusifoliol, a constituent of a folk medicine for treatment of malignant 
      tumors, which also assigns the absolute configuration, illustrates the utility of 
      the method.
FAU - Trost, Barry M
AU  - Trost BM
AD  - Department of Chemistry, Stanford Univeristy, Stanford, California 94305-5080, 
      USA. bmtrost@stanford.edu
FAU - Shen, Hong C
AU  - Shen HC
FAU - Dong, Li
AU  - Dong L
FAU - Surivet, Jean-Philippe
AU  - Surivet JP
LA  - eng
PT  - Journal Article
PT  - Research Support, U.S. Gov't, Non-P.H.S.
PT  - Research Support, U.S. Gov't, P.H.S.
PL  - United States
TA  - J Am Chem Soc
JT  - Journal of the American Chemical Society
JID - 7503056
RN  - 0 (Allyl Compounds)
RN  - 0 (Chromans)
RN  - 0 (Phenols)
SB  - IM
MH  - Alkylation
MH  - Allyl Compounds/chemical synthesis/*chemistry
MH  - Chromans/*chemical synthesis
MH  - Phenols/*chemistry
EDAT- 2003/08/02 05:00
MHDA- 2003/09/30 05:00
CRDT- 2003/08/02 05:00
PHST- 2003/08/02 05:00 [pubmed]
PHST- 2003/09/30 05:00 [medline]
PHST- 2003/08/02 05:00 [entrez]
AID - 10.1021/ja036052g [doi]
PST - ppublish
SO  - J Am Chem Soc. 2003 Aug 6;125(31):9276-7. doi: 10.1021/ja036052g.