Two different approaches toward the synthesis of a 3-acyl-substituted 1,2,3-triphenylcyclopropene were investigated. The first involved treating triphenylcyclopropenyl perchlorate with the anion derived from 1,3-dithiane followed by hydrolysis of the resulting dithioacetal. Unfortunately, all attempts to obtain a carbonyl compound from the hydrolysis failed. The only product obtained corresponded to a 1,2-diphenyl-1,2-diacyl-substituted alkene. The second approach utilized for the synthesis involved treating 3-cyano-l,2,3-triphenylcyclopropene with methyllithium. The addition proceeded quite smoothly to give the desired 3-acetyl derivative in high yield. Irradiation of l,2,3-triphenyl-3-acetylcyclopropene in benzene afforded a mixture of 2,3,4-triphenyl-2-cyclopentenone (60%), 2-methyl-3,4,5-triphenylfuran (27%), and 3-acetyl-1,2-diphenylindene (13%). The formation of the three products obtained can be rationalized in terms of a vinylcarbene intermediate. Several different pathways are available to this species, depending on the stereochemistry about the double bond and on the conformation the oxygen atom assumes in the cis intermediate. The formation of the 2-cyclopentenone derivative provides good support for the mechanism proposed some years ago to rationalize the photochemical rearrangement of 2,5dimethylfuran.
The scope of the thermal [3,3]-sigmatropic rearrangement of a number of 2-allyloxy-substituted 4,5-diphenyloxazoles has been examined. These systems undergo a facile aza-Claisen rearrangement to give 3-allyl-substituted 4,5-diphenyl-4-oxazolin-2-ones. In contrast to the thermal results, irradiation of the 2-allyloxyor benzyloxy-substituted oxazole gave rise to a mixture of 3-and 5-substituted oxazolinones. The photolysis proceeds via C-0 bond scission to generate a radical pair which subsequently recombines to produce the mixture of oxazolinones. A series of related oxazoles was prepared in which the heterocyclic ring and the ir bond are connected by an alkoxy side chain. All attempts to induce an intramolecular Diels-Alder reaction failed. The only product that could be obtained corresponds to that derived from an intramolecular ene reaction. The excited-state behavior of several 2-and 5-allyloxy-substituted oxazoles was also studied. The rationale for the difference in thermal and photochemical behavior is discussed.
JV-Methyl-7-cyanobenzofuro[3^-6]pyridinium Iodide (16). 7-Cyanobenzofuro[3,2-b]pyridine (0.097 g) and methyl iodide (0.213 g) were dissolved in benzene (30 mL) and heated in a Fischer-Porter tube at 100 °C for 3 days. The yellow crystals were filtered (0.165 g, 98%) and recrystallized from methanol (15 mL) to give yellow needles of JV-methyl-7-cyanobenzofuro[3,2-6]pyridinium iodide (0.147 g, 85.7%): mp [285][286][287] °C dec; IR (KBr) 2242 cm"1 1 (C=N); NMR (CFgCOOH) 9.2-8.1 (m, 6 ), 5.03 (s, 3 H, CHg); mass spectrum, m/e 194 ( +• -CHgl).
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