Gerrit J. van Hummel

A novel approach to inherently chiral calix[4]arenes by direct introduction of a substituent at the meta position

A novel method for the preparation of inherently chiral calix[4]arenes is described by direct introduction of a substituent in para-acetamido substituted calix[4]arenes. Bromination and nitration of mono(acetamido)calix[4]arenes 5, 6 afforded calix[4]arenes 7?10, in which the substituent was selectively introduced adjacent to the acetamido moiety, in 58?98% yield. Bromination of bis(acetamido)calix[4]arene 13 gave a mixture from which dibromo- (14) and tribromocalix[4]arene 15 were isolated in 10% and 22% yield, respectively. The structure of 14 was confirmed by single-crystal X-ray structure determination. Nitration of 13 gave 4,16-dinitro- (16) and 4,18-dinitrocalix[4]arene 17 in 53% and 18% yield, respectively.

Selective functionalization of cavitands: synthesis of a new hemicarcerand

Partly bridged cavitands 2 and 4 can be selectively debrominated in one step by treatment with 5 equiv of n-BuLi in THF to afford the corresponding dibromo derivatives 5 and 6 in 90% and 77% yield, respectively. After incorporatin of the fourth bridge, the remaining two bromines can be replaced by CN to give 9 (95%), (C(O)OMe to give 10 (60%) or OH to give 11 (62%). Two molecules of 11 were coupled with CH2BrCl in DMSO/THF under high dilution conditions to give new hemicarcerand 12 in 71% yield.

Proximally Functionalized Cavitands and Synthesis of a Flexible Hemicarcerand

A general study on the synthesis of partly bridged octols3a-d and4c-d is described. Tri-bridged diol3c can be prepared in 54% yield in DMSO at 70°C with excess CH2BrCl or in 52% yield in DMF at 70°C with only 4 equiv. of CH2BrCl. 1,3-Di-bridged tetrol4a, one of the two possible di-bridged isomers formed in preference to the other, was obtained in 30% yield. Tri-bridged diols3c andd can be selectively debrominated in one step by treatment with 5 equiv. ofn-BuLi in THF to afford the corresponding dibromo derivatives8a andb in 77% and 76% yields, respectively. After incorporation of the fourth bridge, the remaining two bromines can be replaced by C(O)OMe to give9c (60%), by OH to give9d (62%) or by CN to give9f (>95%). When the lithiated derivatives of3c andd are quenched with electrophiles other thanH+, a selectively functionalized tri-bridged diol with hydroxyl (8c, 47%) and selectively functionalized cavitands with thiomethyl (9g, 25%) or iodo (9h, 20%) groups can be synthesized. Two molecules of9d were coupled with CH2BrCl in DMSO/THF under high dilution conditions to give the flexible hemicarcerand10 in 71% yield.

Selective functionalization of resorcinarene cavitands; single crystal X-ray structure of a distally functionalized cavitand

A new method for the selective functionalization of resorcinarene cavitands is described starting from tetrakis(bromomethyl)cavitands.

High hyperpolarizabilities of donor-p-acceptor-functionalized calix[4]arene derivatives by pre-organization of chromophores

A systematic investigation of the conceptofpre-organization of nonlinear optical (NLO) active chromophoric groups in calix[4]arene derivatives and the influence on the absolute second-order nonlinear optical coefficients is reported. Several calix[4]arenes were synthesized by modification of the electron-withdrawing groups at the upper rim of the aromatic and extension of the conjugated system of the pre-organized chromophoric groups. Electrical field induced second harmonic generation (EFISH) experiments showed high (0) values up to 1165·10-48 esu. Compared with the corresponding reference compounds, enhancements of the (0) values varying up to 2.5 times per chromophore were observed which proves the benefit of pre-organization of NLO-active units in a multi-chromophoric system. Another important advantage is that the increase in NLO activity observed for these systems is not accompanied with a shift of the absorption band to longer wavelengths exceeding 20 nm. This makes these calix[4]arene derivatives promising building blocks for the development of stable, NLO-active materials that are suitable for frequency doubling.

Structure, twinning, and ferroelasticity of bis(tetramethylammonium) hexafluorotitanate(IV), (TMA)2[TiF6]

Abstract The structure of (TMA)2[TiF6] was determined to be rhombohedral (pseudo-cubic) at room temperature and has been refined to wR = 7.6%. It is isostructural with (TMA)2[OsF6]. Crystals grown from aqueous solution have pseudo-octahedron and pseudo-cube faces and exhibit twinning along pseudo-cubic {110} and {100} planes. Ferroelastic switching of the lattice orientation of a single crystal has been achieved by application of shear stress.

Selective phosphorylation of p-tert-butylcalix[6]arene

The synthesis of selectively phosphorylated and thiophosphorylated p-tert-butylcalix[6] arenes is described; the solid-state structure of the 1,4-bis(thiophosphorylated)p-tert-butylcalix[6]arene is elucidated by X-ray crystallography.

Preparation and X-ray structures of complexes of 18-membered crown ethers with polyfunctional guests: Urea and (O-alkyliso)uronium salts

The preparation and X-ray structure determinations of six complexes of urea and (O-n-butyliso)uronium salts with crown ethers are presented. Urea forms isostructural 5:1 adducts with 18-crown-6 (1) and aza-18-crown-6 (2), in which two urea molecules are each hydrogen bonded to two neighbouring hetero atoms of the macroring. The remaining urea molecules form two-dimensional layers alternating with crown ether layers. In both complexes the macroring has theg+g+a ag−a ag−a g−g−a ag+a ag+a conformation withCi symmetry. In the solid 1:1 complex of O-n-butylisouronium picrate with 18-crown-6 (3) two types of conformations of the macroring were observed: theg+g+a ag−a ag+a ag−g−ag−a ag+a conformation with approximateCm symmetry and to a lesser extent theg+g+a ag−a ag+a g+g+a ag−a ag+a conformation with approximateC2 symmetry. Both conformations allow the guest to form three hydrogen bonds to the macrocyclic host. Three complexes of 18-crown-6 and uronium salts have been prepared and characterized by X-ray crystallography. The 1:1 complexes with uronium nitrate (4) and uronium picrate (5) both exhibit the sameC2 conformation and the same hydrogen bonding scheme as in the least occupied form of the previous complex. A 1:2 complex with uroniump-toluenesulphonate (6) has a different hydrogen bonding scheme (two hydrogen bonds per cation to neighbouring oxygen atoms of the macroring) and a different conformation of the host molecule (theag+a ag−a ag+a ag−a ag+a ag−a conformation with almostD3d symmetry). An attempt to prepare a solid uronium nitrate complex with diaza-18-crown-6 in the same way as the 18-crown-6·uronium nitrate (1:1) complex did not yield the expected result. Instead X-ray analysis revealed that the uronium ion is dissociated, resulting in the nitrate salt of the diprotonated diaza crown ether (7).

Isolation and X-ray crystal structure of a stable calix[4]arene monohemiketal

The formation of a stable calix[4]arene monohemiketal is described. X-ray crystallographic data provide conclusive evidence for the presence of a stabilizing hydrogen bond.

Ring expansion with four C atoms by tandem (2 + 2)cycloaddition and electrocyclic ring opening

A four-carbon ring expansion is presented which involves reaction of enamines of cyclic ketones with methyl propiolate followed by reaction of the resulting cis,cis-cycloalkadienes, also containing an ‘enamine’ type of double bond, with dimethyl acetylenediacarboxylate (DMAD).