4th EucheMs chemistry congress

Poster Session 2
s1295
chem. Listy 106, s257–s1425 (2012)
Poster session 2 - organic chemistry
P - 0 8 6 4
A Boron CAtALyzed ALdoL reACtion
u. hAnefeLd 1 , t. MueLLer 1 , K. dJAnAShviLi 1 ,
i. w. C. e. ArendS 1
1 Delft University of Technology, BOC, Delft, Netherlands
The aldol reaction plays an important role in the formation
of C-C-bonds. A major challenge in the catalytic aldol reaction is
selectivity, since the reaction is immediately followed by the
elimination of water [1] . Boronic acid derivatives were
demonstrated to be valuable catalysts for the aldol reaction;
however they have to be dissolved in water [2, 3] . We developed a
tetrahedral boronate salt, which is soluble in organic solvents.
Therefore we are able to perform the reaction in the substrate,
acetone.
The aldol reactions were performed with our soluble
catalyst, sodium (3,5-difluorophenyl) triisopropoxy boronate.
The Aldol reaction is carried out in a short reaction time with
a good conversion for an electron poor aromatic system. After
20 min. 80 % conversion (38% aldol) was obtained with
4-Methoxybenzaldehyde. Performing the reaction with
benzaldehyde gave good selectivity. After 20 min. 73 % of the
aldol product and 23 % of the elimination product were obtained.
An extensive screening of substrates and reaction conditions will
be presented.
references:
1. R. Mahrwald, Modern Aldol Reactions, Wiley-VCH (2004).
2. Y. Mori, J. Kobayashi, K. Manabe, and S. Kobayashi,
Tetrahedron, 58 (2002) 8263 – 8268.
3. K. Aelvoet, A S. Batsanov, A. J. Blatch, C. Grosjean,
L. G. F. Patrick, C. A. Smethurst and A. Whiting,
Angew.Chem.Int.Ed., 47 (2008) 768 – 770.
Keywords: Catalysis; Solvent free; boron;
4 th EucheMs chemistry congress
P - 0 8 6 5
ProGreSS in the SeArCh for the C-Cn2 CArBene
e. hAnzLovA 1 , t. MArtinu 1 , r. nAvrAtiL 1 ,
C. ShAffer 2 , d. SChrÖder 2
1 Institute of Chemical Technology, Department of Organic
Chemistry, Prague 6, Czech Republic
2 Institute of Organic Chemistry and Biochemistry AS CR,
Molecular Spectroscopy, Prague 6, Czech Republic
Experimental evidence and computational results suggest
that 3-bromodiazirine-3-carboxylic esters (1) undergo anionic
fragmentation to the bromodiazirinyl anion (c-CN Br 2 – ), a weakly
bound complex of the bromide ion and diazirinylidene (c-CN ), 2
formally the simplest N-heterocyclic carbene (NHC) containing
two nitrogen atoms. Esters 1 react with alkoxides to afford the
corresponding carbonates via nucleophilic acyl substitution. The
c-CN Br 2 – leaving group dissociates to the strongly electrophilic
c-CN (cf.the classical nucleophilic NHCs), which is then
2
transformed in the presence of an alcohol to an alkoxymethylene
(ROCH) via a 3-alkoxydiazirine. The ROCH carbene inserts into
the O–H bond of the alcohol resulting in an isolable product,
dialkoxymethane. Additionally, 2-oxabicyclo[4.1.0]heptanes are
formed from the nucleophilic ROCH by an intramolecular
cycloaddition when some 4-alken-1-ols are employed. The
alkoxide cleavage of 1 is always accompanied by the evolution
of N . When the reactions are performed in amidic solvents,
2
mixtures of N and CO result (even under oxygen-free
2
conditions). This observation can be explained by an oxygen atom
transfer from the solvent to the c-CN followed by fragmentation.
2
In the gas phase, collision-induced dissociation (decarboxylation)
of the 3-bromodiazirine-3-carboxylate ion generated from the
ester 1 results in the appearance of a CN Br 2 – ion. The constitution
of this species remains to be determined, however, its facile loss
of the bromide ion agrees well with the proposed precursor of
c-CN . 2
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc