Kenji Hayakawa

Photocyclization of methyl 2-arylthio- and 2-aryloxy-acetoacetates: A facile synthesis of benzoheterocycles

Abstract A series of methyl 2-arylthio- (2) and 2-aryloxy-acetoacetates (3) have been prepared and their tautomeric equilibria have been examined by 1H NMR spectroscopy. S-substitution at the α-position results in an increase of enol tautomer over 90%, while the O-analogues exist predominantly in the keto form (Table 1). Pyrex-filtered irradiation of 2-arylthio compounds 2a-1 in benzene-methanol (1:1) solution gives benzothiophene derivatives (6a–f, 7–10) in fair yield except for 2j and 2k, for which photocyclization does not occur and only polymer formation is observed. A similar irradiation of O-analogues 3b and 3c affords the furan derivatives 17 and 18, respectively, in rather low yield, whereas 3a in photoinert under these conditions. Regiospecificity of photocyclization is revealed by the reactions of 2-naphthyl derivatives (2h and 3c) which afford only naphto[2,1-b] isomer. A plausible reaction mechanism is also discussed.

Synthesis and cycloaddition reaction of 2,3-dimethylene-7-isopropylidenebenzonorborene

Abstract Synthesis of 2,3-dimethylene-7-isopropylidenebenzonorbornene ( 2 ) and its cycloaddition reactions with dichloroketene and dienophiles are described.

Photochemical ring closure of α,α-bisulfenylated carbonyl compounds: Stereoselective formation of cix-dihydrobenzothiophenes

Abstract Photochemistry of α,α-bisulfenylated ketone has been investigated. Irradiation of 2-phenylthiodihydrothiophen-3-one ( 1 ) in benzene gave the radical recombination products 9 (63%) and 10 (49%). In a polar solvent, the ionic chemistry became predominant. Brief irradiation of 1 in acetonitrile and methanol gave the cis -fused dihydrothiophene 11 as the major product in 43% and 20% yields, respectively. The stereoselective photocyclization was generally observed for other ketones ( 2–8 ) in acetonitrile solution (Table 1). The photo-products were easily dehydrated by treating with boron trifluoride etherate to give the corresponding benzothiophenes in high yields. Simple α-phenylthioketones are photoinert under the same conditions. The mechanism of this novel photocyclization of bisulfenylated ketones is also discussed.

Stereospecific photocyclization of α-bisulfenylated keto compounds. Cis-dihydrobenzothiophenes☆

Abstract Irradiation of α-bisulfenylated keto compounds in acetonitrile affords the cis-fused dihydrobenzothiophenes which are dehydrated to benzothiophenes in high yields.

Molecular design by cycloaddition reactions. X. Photochemical cross cycloaddition of 1,3-diphenylisobenzofuran to cycloheptatriene

I,3-Diphenyl-isobenzofuran (I) reagiert mit Cycloheptatrien (II) uber diskutierte Zwischenstufen zu Mischungen aus den Addukten (IV)-(VII) neben dem Dimeren (III).

Photocyclization of methyl 2-arylthioacetoacetates a facile synthesis of benzothiophenes

Abstract A series of methyl 2-arylthioacetoacetates was irradiated in a benzene-methanol solution to give benzothiophenes in satisfactory yields.