Robert S. Sheridan

A reinvestigation of the meta—photoadditions of cyclooctene to anisole and toluene

Abstract The meta-photoadditions of cis-cyclooctene to anisole and toluene are shown to proceed via 2,6-bonding to the aromatic rings, in contrast to previous reports.

Photochemical Diels-Alder addition of N-methyltriazolinedione to phenanthrene

Abstract Visible irradiation of solutions of N-methyltriazolinedione and phenanthrene results in several Diels-Alder type adducts. The mechanism for these photoadditions is discussed.

Regiochemical substituent switching of spin states in aryl(trifluoromethyl)carbenes.

Although aryl(trifluoromethyl)diazirines have achieved great popularity in photoaffinity labeling applications, the properties of the corresponding carbenes have not been as widely explored. Here, low-temperature matrix-isolation spectroscopy and reactivity studies indicate that in contrast to m-methoxyphenyl(trifluoromethyl)carbene and most known aryl(CF(3))carbenes, the para isomer is a ground-state singlet rather than triplet. DFT calculations support these results as well as the notion that the p-CH(3)O group stabilizes the singlet carbene via resonance. These results may have relevance to the wide range of substituted aryl(CF(3))diazirines in photoaffinity applications.

ADAMANTYLCHLOROCARBENE : CHARACTERIZATION AND REARRANGEMENT TO CHLOROHOMOADAMANT-3-ENE

Abstract Adamantylchlorocarbene and its ring-expanded product, chlorohomoadamant-3-ene, have been characterized by matrix isolation spectroscopy combined with DFT calculations.

Synthesis and reaction of 2,3-diazabicyclo[2.2.1]hept-5-ene

Abstract The first synthesis of 2,3-diazabicyclo[2.2.1]hept-5-ene is reported. The generation of this molecule is facilitated by the isolation of the bis-carboxylate salt formed on hydrolysis of the corresponding biscarbamate. The retro-Diels-Alder generation of diimide and cyclopentadiene is explored.

Photochemical ring expansion of tetramethylcyclobutanone revisited: angular dependence of electronic absorption of singlet carbenes

Tetramethyltetrahydrofuranylidine, produced by the photochemical ring expansion of the corresponding cyclobutanone, has been characterized by IR and UV/Vis spectroscopy in a low-temperature N2 matrix. The angular dependence of the UV/Vis spectra of this and related carbenes is explored by ab initio calculations. Carbene 2 was characterized in N2 at 12 K by IR and UV/Vis. Ab initio calculations were performed to investigate the difference between the UV/Vis of 2 vs. other oxycarbenes.

Methoxy as a removable activating group in the triazolinedione rearrangement route to azo compounds

Abstract A methoxy group dramatically increases the yield of stepwise homo-Diels-Alder additions of N-methyltriazolinedione to aromatic meta-photoadducts, and can conveniently be subsequently replaced by other substituents.

Matrix isolation and photochemistry of 1- and 2-naphthylchlorocarbene

We have for the first time characterized the 1- and 2-naphthylchlorocarbenes by IR and UV/vis spectroscopy in N2 matrices at 10 K. Although evidence suggests the presence of predominantly only one geometric isomer in the case of the 1-naphthylchlorocarbene, the IR and UV/vis spectra of the 2-naphthylchlorocarbene indicate two distinct conformations. With selective irradiation, the longer-wavelength absorbing s-Z-isomer of 2-naphthylchlorocarbene can be photochemically driven to the alternate s-E conformation. Irradiation of the 1- and 2-naphthylchlorocarbenes induces cyclization to 7-chloro-4,5-benzobicyclo[4.1.0]hepta-2,4,6-triene and 7-chloro-2,3-benzobicyclo[4.1.0]hepta-2,4,6-triene, respectively. The cyclization can be reversed by irradiation at shorter wavelengths.Our results on the singlet naphthylchlorocarbenes photochemical ring-closures parallel observations of Chapman, McMahon, and co-workers on the parent triplet 1- and 2-naphthylcarbenes (P. R. West, A. M. Mooring, R. J. McMahon and O. L. Chapman, J. Org. Chem., 1986, 51, 1316; S. W. Albrecht and R. J. McMahon, J. Am. Chem. Soc., 1993, 115, 855). In particular, under matrix isolation conditions, the naphthylcarbenes appear to photochemically only cyclize to the corresponding cyclopropenes, which in turn only photochemically ring-open back to the carbenes. Ring-expansion in these systems to benzocycloheptatetraenes is not detected.

Stereochemical Evidence of Dual Chemoreceptors for an Achiral Sex Pheromone in Lepidoptera

Abstract The racemate and optically pure enantiomers of 9-(cyclopent-2-en-l-yl)nonyl acetate have been synthesized and found to mimic certain biological properties of a natural sex pheromone, Z -11-tetradecenyl acetate, European corn borer and redbanded leaf rollers respond differently to the racemate and to the enantiomers in precopulatory-behavior bioassay. The bioassay results demonstrate the resence of two stereospedfic chemoreceptors for the achiral pheromone, the chiral character of these chemoreceptors, and define the conformation of carbon atoms 10–14 of Z -ll-tetradecenyl acetate in each receptor. Specificity in communication is the adaptive advantage the insect gains by using two stereospedfic chemoreceptors with different conformational requirements for the achiral pheromone. The methodology described provides a new tool for neurochemical investigation of chemical sensing. A correlation of specific rotation and molecular weight is demonstrated for 3-subst1tuted cyclopentenes.