Ihsan Erden

Chemistry of singlet oxygen: Isolation and characterization of a stable allene oxide from a fulvene endoperoxide☆

Abstract Decomposition of the saturated endoperoxide derived from 6- t -butylfulvene at 1OO°C gives a stable allene oxide which was isolated and characterized by spectroscopy and chemical transformations. The thermal isomerization of the parent unsaturated system is also described and the decomposition mechanisms are discussed.

Thermal decomposition of 7-isopropylidene-2,3-dioxabicyclo[2.2.1]heptane: Evidence for allene oxide and cyclopropanone intermediates☆

Abstract The saturated endoperoxide derived from 6,6-dimethylfulvene was shown to be a unique source of an allene oxide and a cyclopropanone: inter- and intramolecular trapping experiments provided permissive evidence that such intermediates are indeed operative in the thermal isomerizations of fulvene endoperoxides.

Cycloadditions of Methylenecyclopropanes and Strained Bicyclo[n.1.0]alkanes To Radicophilic Olefins

Abstract The methylenecyclopropanes 1, 2, 11 upon reaction with α-donorsubstituted acrylonitriles 3a, 3c gave two types of products, regular [2+2] cycloadducts 6, 8, 10, 13, 14 and thiacyclopentane derivatives 7, 9. The capto-dative substituted methylenecyclopropane 12 preferentially homodimerized to 15 even in the presence of 2 . The capto-dative olefin 3a also added across the central single bonds of a bicyclo[1.1.0.]butane derivative 4b and bicyclo[2.1.0]pentane 5a to yield 16 and 19 via diradical intermediates.

Photooxygenation of bicyclopropylidene

Abstract Upon photooxidation bicyclopropylidene ( 1 ) yields spiro[2.3]hexan-4-one ( 4 ) and 7-oxatrispiro[2.0.2.1]heptane ( 6 ). The formation of these is rationalized. Authentic 6 was prepared by epoxidation of 1 , and 4 by isomerization of 6 .

1,2-Dihydropentalenes from Fulvenes by [6 + 2] Cycloadditions with 1-Isopropenylpyrrolidine

In situ generated acetone pyrrolidine enamine undergoes [6 + 2] cycloadditions with fulvenes to give 1,2-dihydropentalenes. This ring annulation method works particularly well with 6-monosubstituted fulvenes and is subject to steric hindrance at C-6 of the fulvene. On the basis of mechanistic studies, optimal conditions have been developed for a one-pot synthesis of 1,2-dihydropentalenes using catalytic amounts of pyrrolidine.

Convenient new synthesis of snoutene [1] utilizing a dipolar cycloaddition of 4-phenyl-1,2,4-triazolin-3,5-dione☆

Abstract 4-Phenyl-1,2,4-triazolin-3,5-dione readily cycloadds to Nenitzescus hydrocarbon 1 [6] with skeletal rearrangement. The major adduct 6 can conveniently be transformed to the azo compound 8 , which upon photolysis or thermolysis yields up to 80 % pentacyclo[3.3.2.02,4,.03,7.o6,8]dec-9-ene (“ snoutene ”).

A Simple Synthesis of [3]-Rotane

Abstract A convenient procedure for the synthesis of [3]-rotane starting from bicyclopropylidene is described.

Triphenylphosphine reduction of saturated endoperoxides.

Triphenylphosphine reduction of saturated endoperoxides derived from 6,6-dimethylfulvene and spiro[2.4]hepta-4,6-diene in the presence of nucleophiles results in the formation of products that mainly stem from deoxygenation followed by carbocation formation. Nucleophilic attack by solvent proceeds by an S(N)1 like mechanism; allyl shifts and cyclopropylcarbinyl-cyclobutyl rearrangements also occur. With the systems lacking carbocation-stabilizing groups, the deoxygenation step is preceded by attack of H(2)O at the phosphorus.

Intermediates in the dye-sensitized photooxygenation of nitrones and hydrazones

Abstract In the dye-sensitized photooxygenation of C-aryl nitrones and hydrazones, short-lived peroxidic intermediates are observed. Their characterization, mechanisms leading to them, as well their decomposition pathways are discussed.

Chemistry of singlet oxygen. Dye-sensitized photooxygenation of arylallenes

Abstract 1-Arylallenes react with singlet oxygen via 1,2-and 1,4-cycloaddition modes giving rise to three types of carbonyl fragments. 1,1-Diphenyl- and 1-methyl-1-phenylallenes react predominantly by the 1,4-mode. Plausible mechanisms are discussed for the formation of the observed products.