The solution-phase synthesis of organic compounds as mixtures rather than in individual pure form offers efficiency advantages that are negated by the difficulty in separating and identifying the components of the final mixture. Here, a strategy for mixture synthesis that addresses these separation and identification problems is presented. A series of organic substrates was tagged with a series of fluorous tags of increasing fluorine content. The compounds were then mixed, and multistep reactions were conducted to make enantiomers or analogs of the natural product mappicine. The resulting tagged products were then demixed by fluorous chromatography (eluting in order of increasing fluorine content) to provide the individual pure components of the mixture, which were detagged to release the final products.
Cationic aqua complexes are prepared from a trans-chelating
tridentate ligand, (R,R)-4,6-dibenzofurandiyl-2,2‘-bis(4-phenyloxazoline) (DBFOX/Ph), and
various transition-metal(II) perchlorates. These
complexes are effective catalysts in the Diels−Alder reactions of
cyclopentadiene with 3-alkenoyl-2-oxazolidinone dienophiles and show excellent enantioselectivities.
The active catalyst complex prepared from
nickel(II) perchlorate hexahydrate has an octahedral structure
with three aqua ligands, and it can be isolated
and stored for months without loss of catalytic activity.
Iron(II), cobalt(II), copper(II), and zinc(II)
complexes
are similarly active. The absolute configuration induced in the
reaction can be readily predicted on the basis
of the C
2-symmetric structure of the complexes
as well as the simple structure of the substrate complex.
The
aqua complex prepared from Ni(II) or Zn(II) perchlorate
results in highly effective chiral amplification in the
Diels−Alder reaction. Use of the DBFOX/Ph ligand of a low
enantio purity of 20% ee leads to a 96% ee for
the endo cycloadduct. Two mechanisms for amplification are
involved in this remarkable chiral amplification: (1) precipitation of an S
4-symmetric meso
2:1 complex between DBFOX/Ph and Ni(II) ion and (2)
associative formation of 1:1 heterochiral complexes by the aid of
hydrogen bonds based on aqua ligands to
produce stable meso oligomers.
Cascade reactions of 4-alkenyl iodides, involving a carbonylation-cyclization-carbonylation sequence, were accomplished by a hnu/Pd system. The stereochemical outcomes suggest that radical carbonylation and subsequent acyl radical cyclization may be involved in this reaction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.