Pentenone

Distal ring-opening is also observed in the intramolecular 3+2 cycloaddition reaction of a 3-pentenone diphenylmethylenecyclopropane derivative in the presence of bis(diben-zylideneacetone)palladium/tri-isopropyl phosphite catalyst, affording regioselectively a diphenylmethylene pentalenone system (equation 360)424. Similarly, thermal cyclization of... 

Cycloaddition 2,5-dialkylcyclo-3-pentenones.1 In the presence of Fc(CO)s or Fc2(CO)<), diallcncs (1) react with carbon monoxide to give 2,5-dialkylidcnc-3-cyclopentenoncs 2 in surprisingly good yield. 

Annelation. McKenzie has reported a modification of the annelation procedure of Caine and Tuller (2, 111-112) that permits this dihalobutene to lx used as a 3-pentenone equivalent. The acetylenic intermediate 2 is obtained as in the Caine method, but this is alkylated before hydration of the triple bond and cyclization to the final product (3). 

Methyl-3-Pentenone-2 Isopropyl idone Acetone Methyl Isobutenyl Ketone... 

The 1,3-dimethyloxyallyl cation, generated in situ by treatment of 2,4-dibromo-3-pentenone with copper and sodium iodide. 

Scheme 15.19 Electrochemical coupling between 3-pentenone and a,a-dichloroester.

Bicycloheptanones formed by intermolecular cycloaddition of 2-cyclo-pentenones to olefins, as in (4.53) 465), are valuable synthons in organic chemistry 454a). 

Placing the electron deficient migration terminus within the original carbonyl partner converts the 1,1-cyclobutanone annulation into a 1,2- or lateral cyclo-pentenone annulation as summarized in Eq. 77. In the ring enlargement of 65 to 66,... 

The intermolecular PKR of an allenic compound with an alkyne Co2(CO)6 complex takes place under very mild conditions when N-methylmorpholine oxide (NMO) is used as a promoter, giving rise to ( )-4-heptylidene-2,3-dipropyl-2-cyclo-pentenone in 69% yield (Scheme 16.48) [50-53],... 

Synonyms AI3-07702 BRN 1361550 Caswell No. 547 EINECS 205-502-5 EPA pesticide chemical code 052401 FEMA No. 3368 Isobutenyl methyl ketone Isopropylidene acetone Methyl 2,2-divinyl ketone Methyl isobutenyl ketone Methyl 2-methyl-1-propenyl ketone 2-Methyl-2-pentenone-4 2-Methyl-2-penten-4-one 4-Methyl-2-penten-2-one NSC 38717 UN 1229. 

Methyl-4-pentanone, see 4-Methyl-2-pentanone 2-Methylpentene, see 2-Methyl-l-pentene 4-Methyl-4-pentene, see 2-Methyl-l-pentene 2-Methyl-2-pentenone-4, see Mesityl oxide 2-Methyl-2-penten-4-one, see Mesityl oxide... 

Triazolylcyclopropane derivatives are endowed with antimycotic properties [125]. They are also prepared as plant growth regulators and fungicides for instance 93 (R = unsubstituted and substituted aryl, heteroaryl) markedly inhibited the growth of rice, cotton and soybeans in hot tests [126]. l-(l,2,4-Triazolyl)-2-(2,4-dichlorophenyl)cyclopropane 94, is a more effective fungicide against Podosphaera leucotricha and a better growth retardant in rice and soybeans than the (l,2,4-triazolyl)pentenone 95, Eq. (36) [127]. 

A similar but different mechanism has also been proposed for the intermolecular CO-SiCaC reaction of phenylacetylene catalyzed by Rh4(CO)i2, which gives silylcyclo-pentenone 9a and 9b (Scheme 7.5) [14]. In this mechanism /9-silylethenyl-[Rh] intermediate Il.lg, arising from insertion of the alkyne moiety into the Si-[Rh] bond, reacts sequentially with a second molecule of phenylacetylene and CO, to afford <5-silylpenta-dienoyl-[Rh] complex II. Ih- Finally, carbocyclization followed by double-bond migration gives 9 a and 9 b. 

In a study of the photoisomerization of 4,4-dimethyl-2-cyclohexenone (8) to 6,6-dimethylbicyclo[3.1.0]-hexane-2-one (9) and 3-isopropyl-2-cyclo-pentenone (10), Chapman and Wampfler48 accounted for the pronounced effect of sensitizer concentration by such a self-quenching mechanism. The phenomenon was exhibited by four ketones with () lowest triplet states but not by benzophenone or acetophenone which have (w, n) triplet states.49... 

Photochemical ring opening of 4,5-epoxy-2,3,4,5-tetraphenyl-2-cyclo-pentenone (66 R = = Ph) (prepared by oxidation of... 

Dlsubstituted 2-cycbpentenones. Cross-conjugated dienones, or the corresponding ethylene kelals, are cyclized almost entirely to 2,3-disubstituted 2-cyclo-pentenones by H3P04-HCOOH (1 1) or HBr-CHjCOOH (1 3). 3,4-Disubstiluted 2-cyclopentenones are formed, if at all, in low yield. 

Oxidative demage offuranes. Alkylfuranes of type 1 are oxidatively cleaved by PCC to cis-1,4-enediones (a), which isomcrizc in the acidic medium to the more stable trans-isomers (2). These products are converted into 4-methoxycyclo-pentenones (3) in methanolic sodium hydroxide. The yields are lower (50 60%) in this sequence when R1 = II. 

The photochemical reactions of three a/3-unsaturated cyclic ketones have been reported. In these cases, it appears that the reaction is that of the olefinic group although the wavelength of the incident radiation is at the ultraviolet absorption of the carbonyl group. Photolysis of 2-cyclo-pentenone (16), carvone (XXXV) (7,12) and y-tropolone methyl ether... 

Upon irradiation, the pyrrolinone 35 undergoes a-cleavage to give the ethoxycyclopropyl carbamate 36 (70%).36) This reaction resembles that of 5,5-diphenyl and 5,5-dimethyl-2-cyclopentenone 37>, which yields cyclopropane derivatives under conditions normally leading to 2-cyclo-pentenone dimers. 38>. 

Cheap and readily available L-proline has been used numerous times for the intermediate and reversible generation of chiral iminium ions from a,/ -unsaturated carbonyl compounds. For example, Yamaguchi et al. reported in 1993 that the rubidium salt of L-proline catalyzes the addition of di-iso-propyl malonate to the acyclic Michael acceptors 40a-c (Scheme 4.13), with enantiomeric excesses as high as 77% [22], With 2-cycloheptenone and 2-cyclohexenone as substrates ca 90% yield and ee of 59% and 49% were obtained. Later the enantioselectivity of this process was increased to a maximum of 88% ee in the addition of di-tert-butyl malonate to the E-pentenone 40a in the presence of 20 mol% Rb-L-prolinate and 20 mol% CsF [23], Taguchi and Kawara employed the L-proline-derived ammonium salts 41a and... 

Although the optically active 4-hydroxycyclo-2-pentenone (73a) is a very important starting material of synthesis of prostaglandins, it is not easy to obtain optically pure 73a efficiently. The biphenanthrol host 15 was found to be a good... 

The effect of reaction time on the major components of the reaction of cystine and DMHF in water is shown in Table IV. It is noteworthy that amounts of 2,4-hexanedione, 3,5-dimethyl-l,2,4-trithiolanes and thiophenones were found at a maximum after one hour. It was also found that the amount of 2-acetylthiazole increased with time and that acetol acetate decreased with time as expected. In the glycerol medium, the effect of reaction time on the major components is shown in Table V. Apparently, the 1,3-dioxo-lane, which is a ketal formed from glycerol and acetone, decreased over time. Also, long reaction time favors the formation of cyclic compounds, including 2,5-dimethyl-2-hydroxy-3(2H)-thiophene, cyclo-pentenones and 4,5-dimethyl-l,2-dithiolenone. 

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