Tze-Lock Chan

Direct conversion of dipropargylic sulfones into (E)- and (Z)-hex-3-ene-1,5-diynes by a modified one-flask Ramberg-Bäcklund reaction

Abstract ( E )- and ( Z )-enediynes 7 are readily synthesized in good yields from a one-pot modified Ramberg-Backlund reaction from dipropargylic sulfones 5 .

SYNTHESIS AND CHIROPTICAL PROPERTIES OF AXIALLY CHIRAL, BINAPHTHOL-BASED OLIGOMERS

Abstract Optically active, axially chiral binaphthol-based oligomers 2 to 4 were synthesized via Hays coupling from the monomer 1 . These oligomers exhibited moderate optical rotation enhancement but the effect quickly reaches a plateau with the tetramer 4 .

X-Ray crystallographic study of guest–molecule orientations in the β-hydroquinone clathrates of acetonitrile and methyl isocyanide

Redetermination of the crystal structure of the Type III β-hydroquinone–acetonitrile clathrate, 3C6H4(OH)2·CH3CN (1), from new Mo-Kα diffractometer data confirmed the principal finding of previous studies, namely that the three symmetry-independent acetonitrile molecules fit snugly inside clathration cavities in a pseudo-rhombohedral host lattice (space group P3), with one guest molecule aligned in the opposite sense to the other two. A parallel study of the potentially isomorphous β-hydroquinone–methyl isocyanide clathrate, 3C6H4(OH)2·CH3NC (2), showed that it is a Type II clathrate (space group R3), in which all three guest molecules in the unit cell are equivalent and point in the same direction parallel to the c axis. The effective molecular length (linear molecular skeleton plus the sum of appropriate van der Waals radii at both ends) of CH3NC is inferred to be ca. 0.1 A longer than that of CH3CN, in keeping with the relative stabilities and unit-cell dimensions of (1) and (2). Lattice parameters are: for (1), a= 16.003(2), c= 6.245(2)A; for (2), a= 15.946(2), c= 6.348(2)A. The structures have been refined to R values of 0.080 (1) and 0.056 (2) using, respectively, 1 277 and 600 observed reflections.

A stable derivative of cyclooctatrienyne: Synthesis and crystal structures of 1,4,7,10-tetramethyl-5,6-didehydrodibenzo[a,e]cyclooctene and 1,4,7,10-tetramethyldibenzo[a,e]cyclooctene

Abstract A stable derivative of cyclooctatrienyne (1), namely 1,4,7,10-tetramethyl-5,6-didehydrodibenzo-[a,e]cyclooctene (3), has been synthesized and fully characterized. X-Ray crystallographic analyses indicate that 3 adopts a “butterfly” conformation intermediate between those of virtually planar 5,6-didehydrodibenzo-[a,e]cyclooctene (2) and tub-shaped 1,4,7,10-tetramethyldibenzo[a,e]cyclooctene(16). The methyl substituents effectively shield the otherwise rather exposed strained triple bond of 3 and kinetically stabilize it against dimerization and/or air oxidation.

Structural studies of some derivatives of cis, cis-cyclohexane-1,3,5-tricarboxylic acid

Abstractcis,cis-Cyclohexane-1,3,5-tricarboxylic acid (1) its trimethyl ester (2) and their 1,3,5-trimethylated and 1,3,5-tribenzylated derivatives were prepared, and their structures studied by two-dimensional NMR spectroscopy in conjunction with X-ray crystallography. The results show that these molecules adopt a chair conformation in solution, with all the carboxyl groups in1 and all the methoxycarbonyl groups in2 occupying the equatorial positions, but with the corresponding functionalities in the alkylated derivatives occupying the axial positions. For2, its 1,3,5-tribenzylated derivative4, andcis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid (5), the same conformational preferences are seen to persist in the crystalline state as in solution.

The synthesis of presumably planar conjugated 8-membered ring compounds

Abstract Using mainly base dehydrobromination reactions of carbocyclic 8-membered bromides, a variety of acetylenic and cumulenic compounds were isolated or postulated as transient intermediates. The physical and chemical properties of the isolable presumably planar 8-membered ring compounds were investigated. Trapping experiments were used to confirm the transitory existence of the unstable intermediates.

1,4,7,10-tetramethyl-5,6-didehydrodibenzo[a,e]cyclooctene. A presumably planar fully conjugated eight-membered ring compound

Abstract The first known stable crystalline derivative of 5,6-didehydrodibenzo [ a,e ] cyclooctene (1), namely, 1,4,7,10-tetramethyl-5,6-didehydrodibenzo [ a,e ] cyclooctene (2), was prepared and unequivocally characterised.

Synthesis and characterization of oligo(2,7-biphenylenylene-(E)-vinylene)s

The syntheses, spectral behavior, and electrochemical properties of novel oligo(2,7-biphenylenylene-(E)-vinylene)s (OBPVs) 1 to 3 have been reported. On the basis of the spectral analysis of OBPVs, a band gap of 2.5 ev for poly(2,7-biphenylenylene-(E)-vinylene) was estimated.

Trapping the elusive 3-thioallophanate ion in a hydrogen-bonded host lattice

The hitherto unknown 3-thioallophanate ion has been generated in situ and stabilized by hydrogen bonding with thiourea in the host lattice of the new inclusion compound [(n–C4H9)4N+]H2NCSNHCO2−·(NH2)2CS.

Stereoselective synthesis of substituted 1,3,5-hexatrienes from diallylic sulfones

Substituted 1,3,5-hexatrienes 7 can be prepared in excellent yields and with good stereoselectivity from diallylic sulfones 6 employing a modified Ramberg–Backlund reaction.