4th EucheMs chemistry congress

wednesday, 29-Aug 2012
s767
chem. Listy 106, s587–s1425 (2012)
organic Chemistry, Polymers – i
General synthetic methods – ii
o - 3 5 9
hydroGenAtion of heteroCyCLiC
CALixAreneS
r. neier 1 , G. Journot 1 , L. CeriSoLi 2 ,
A. GuALAndi 2 , d. SAvoiA 2
1 University of Neuchatel, Department of Chemistry, Neuchatel,
Switzerland
2 University of Bologna, Department of Chemistry, Bolgona, Italy
The simple and efficient synthesis of calix[4]furan and
calix[4]pyrrole has been known for more than 125 years. The
connectivity of the heterocyclic calix[4]arenes is identical with
the skeleton of the «pigments of life». The chemical properties,
especially the ability to form complexes with transition metals,
are totally different when comparing the artificial systems with
the natural products. A direct way to confer metal binding
capabilities to compounds derived from heterocyclic
calix[4]arenes is hydrogenation. We present our systematic studies
of the hydrogenation reactions of calix[4]furan and
calix[4]pyrrole. The hydrogenation of the calix[4]pyrrole proved
to be challenging. The major products obtained first were the half
reduced macrocycles of the type calix[2]pyrrole[2]pyrrolidine.
The totally reduced macrocycle was isolated only in small
amounts. To understand the sequence of this heterogenous
catalytic hydrogenation the synthesis of mixed calix[n]furan[4-
-n]pyrrole was undertaken. These mixed macrocycles were good
model compounds for studying the sequence of the reduction
process. The macrocycles were preferentially hydrogenated on
the furan rings, whereas the hydrogenation of the pyrrole rings
consistently needed much harsher conditions. Exploiting this
difference in reactivity we were able to determine the sequence
of the hydrogenation reaction. Based on these mechanistic data
an improved synthetic procedure has been developed for the
hydrogenation process, which allowed us to obtain the totally
reduced macrocycle calix[4]pyrrolidines in quantitative yield. The
calix[2]pyrrole[2]pyrrolidine showed a very strong intramolecular
hydrogen bond network. This network determines the structure,
the conformational behavior and the chemical reactivity of
this novel macrocycle. The metal binding of the totally
reduced calix[4]pyrrolidines will be presented. The new
calix[4]pyrrolidines can be classified as new stiffened macrocyclic
crown ethers or as saturated analogues of the porphyrin derived
«pigments of life».
Keywords: Heterogenous catalysis; Calixarenes;
Hydrogenation; Hydrogen bonds; Heterocycles;
General synthetic methods – ii
4 th EucheMs chemistry congress
o - 3 6 0
one-Pot nuCLeoPhiLiC rAdiCAL Addition to
KetiMineS GenerAted in Situ
B. roSSi 1 , n. PAStori 1 , A. CLeriCi 1 , S. ProSPerini 1 ,
C. PuntA 1
1 Politecnico di Milano, Dipartimento di Chimica Materiali ed
Ingegneria Chimica “G. Natta”, Milano, Italy
In the last years we reported that the Ti(III)/hydroperoxide
(H O , t-BuOOH) system was able to promote both radical
2 2
Mannich-type reactions and a radical version of the Strecker
synthesis, starting from an aldehyde and an amine in ether, alcohol
or formamide co-solvent, respectively. [1] The optimization of the
previously reported protocol allowed us to develop the
nucleophilic free radical addition of formamide to ketimines
generated in situ by replacing the aqueous solution of TiCl with 3
the more convenient and efficient Ti(IV)-Zn system, providing
instant access to quaternary α-aminonacid precursors. [2, 3] The new
catalytic system was successfully applied for the nucleophilic
radical hydroxymethylation of ketimines, leading to the synthesis
of β-amino alcohols [4] and the selective radical aminoalkylation
of ethers. [5]
references:
1. a) Cannella, R.; Clerici, A.; Panzeri, W.; Pastori, N.; Porta,
O. Tetrahedron 2006, 62, 5986–5994;
b) Clerici, A.; Ghilardi, A.; Pastori, N.; Punta, C.; Porta,
O. Org. Lett. 2008,10, 5063–5066;
c) Cannella, R.; Clerici, A.; Panzeri, W.; Pastori, N.; Punta,
C.; Porta, O. J. Am. Chem. Soc. 2006, 128, 5358–5359.
2. Pastori, N.; Greco, C.; Clerici, A.; Porta, O. Org. Lett.
2010,12, 3898–3901.
3. Prosperini, S.; Pastori, N.; Ghilardi, A.; Clerici, A.; Punta,
C. Org. Biomol. Chem., 2011, 9, 3759-3767
4. Rossi, B.; Pastori, N.; Clerici, A.; Punta, C., submitted.
5. Rossi, B.; Pastori, N.; Clerici, A.; Punta, C. manuscript in
preparation.
Keywords: Radical reactions; Titanium; Multicomponent
reactions; Nucleophilic addition; Amino alcohols;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc