Shaw-Tao Lin

Analysis of Substituent Effects on C-13 NMR Parameters of Substituted Arylacetylene Derivatives. Linear Free Energy Relationships and PM3 Semiempirical Calculations

Abstract The substituent-induced chemical shifts (SCS) of C(α,β) on the 13C NMR spectra of arylalkynes (i.e. containing H, CH3, Cl and Br) were studied. The correlation between SCS and Hammett constants shows that the tendency of the effect by the substituents on the phenyl ring is Br (ρ=8.15)>Cl (ρ=7.27)>CH3 (ρ=6.79)>H (ρ=5.78). This order can be rationalized as due to the ability of the group on the alkyne to stabilize the partial positive charge on C(β) resulting from polarization with π electron transfer from C(β) to the phenyl ring. The SCS values are also well correlated with the electron densities obtained from PM3 calculations. The solvent effect on the 13C chemical shifts of phenylalkynyl bromide demonstrates a strong dependence on the relative permittivity as well as the shielding character of the solvents.

Preparation of 3e,4,5,6e,7,8-hexahydro[2.2]paracyclophane

Abstract 3e,4,5,6e,7,8-Hexahydro[2.2]paracyclophane (11) was prepared through a coupling reaction to form dithiacyclophane, oxidation to yield the sulfone followed by the pyrolysis. It is noteworthy that the methine hydrogen in the rigid structures 5 and 11 toward to the center of the benzene ring leading to high field shifts resonance appear at δ −0.72 and −2.32 ∼ −2.41.

Preparation of 1-Aryl-2-bromo-3,3-difluorocyclopropenes

1-Aryl-2-bromo-3,3-difluorocyclopropanes were prepared from the reaction of 2′,2′-difluorostyrene and dibromocarbene instead of from 1-aryl-2-haloacetylenes and difluorocarbene. These results are rationalised by the energy gap between HOMO(styrene), HOMO(acetylene) and LUMO(CX2). The title compounds were converted to methyl arylpropynoate in MeOH solution in quantitative yield.

Mass spectra of 3,3‐difluoro‐1‐halo‐2‐arylcyclopropenes

The electron ionization (EI) mass spectra of a series of 3,3-difluoro-1-halo-2-arylcyclo- propenes (1, 2) give the fragments [M-X](+) (X: Br, Cl) as the base peaks. A comparison of tandem mass spectrometry (MS/MS) profiles of the m/z 151 ions recorded from compounds 1 and 2 and 3-bromo-3,3-difluoro-1-phenylcyclopropyne (5), 1,1,2,2-tetrafluoro-3-phenyl- cyclopropane (6), 1,1,2,2-tetrafluoroindane (7), and 2,3,3-trifluoroindene (8) suggested that the structure of the derived [M-X](+) fragment ion is more likely that of a substituted cyclopropenium ion. The results from calculations using the density functional theory (DFT) method support this MS/MS analysis.

Preparation of arylspiro[2.4]hept-5-enes from aryldibromocyclopropanes via diallylation and metathesis reaction

A series of arylspiro[2.4]hept-5-enes can be prepared from aryl-diallylcyclopropanes by using Grubbs’ catalyst in good yields.

Preparation and spectroscopic study of 13-substituted 2,11-dithiahexahydro[3.3]paracyclophanes

A series of 13-substituted 2,11-dithiahexahydro[3.3]paracyclophanes each containing a substituent on the benzene ring were prepared for 1H NMR and X-ray diffraction analyses. The benzene ring and the cyclohexane ring demonstrate shielding of the hydrogen(s) of the opposite ring. The benzene ring is distorted by the substituent on that ring.

Preparation of [2.2]-para-, meta-, and ortho-cyclophanes containing a 1,3-cyclohexano group

[2.2]-para-, meta-, and ortho-Cyclophanes containing a 1,3-cyclohexane ring bridged with two carbons were prepared through a coupling reaction to form dithiacyclophane, followed by oxidation to yield the sulfone and then pyrolysis.

Preparation of [2.2]meta- and ortho-Paracyclophanes Containing the Cyclohexano Group

[2.2]Metaparacyclophane (20, cis-tricyclo[9.2.2.14,8]octadeca-4,6,8(16)-triene) and [2.2]orthoparacyclophane (22, cis-tricyclo[10.2.2.04,9]octadeca-4,6,8-triene) containing a 1,4-cyclohexano group bridged with two carbons are prepared through a coupling reaction to form the dithiacyclophanes, oxidation yields the sulfones followed by pyrolysis.

3-Aryl-3-hydroxy-2,2,4,4-tetramethylcyclobutanones and Related Compounds.

3-aryl-3-hydroxy-2,2,4,4-tetramethylcyclobutanones and 1-aryl-2,2,4-trimethyl-1,3-pentadiones were prepared from arylation of 1,1,3,3-tetramethyl-5,8-dioxapiro [3,4]octan-2-one followed by hydrolysis using THF and HCl respectively.

Oxidation of 3-Aryl-4-(1-hydroxyethyl)sydnones using DMSO-Ac2O as Oxidant

Treatment of 3-aryl-4-(1-hydroxyethyl)sydnones with DMSO-Ac2O yielded esters and ketones, depending on the amount of Ac2O used; application of a limited amount of Ac2O with DMSO as an oxidant has been found to be the only method to convert the title compounds to the ketones.