A,/i-Epoxy ketones

The cleavage-ehmination of a,i -epoxy ketones (section XIII is similar other examples are given in ref. 126, 127, 128, and 369,... 

On addition of SO4 - to the triple bond in the 10-member cycloalkyne 24 and cyclo-alkynone 27, a nonchain, and anionic, self-terminating radical cyclization cascade is induced. In the former reaction (equation 22) the bicyclic ketones 25 and 26 are formed, and in the latter reaction (equation 23) the a,/i-epoxy ketones 28 and 29 are formed in good yields. Because of the difficulty of oxidizing isolated triple bonds, SCh - does not react as an electron-transfer reagent in these reactions but acts as a donor of atomic oxygen. 

Cleavage of a,[i-epoxy ketones.1 The reagent (1), possibly (CH3)2SC1, formed from DMSO and ClSi(CH3)3, cleaves a,(3-epoxy ketones to 2-chloro-3-hydroxy ketones with high regioselectivity (equation I). If the epoxide has a phenyl substituent, 3-chloro-2-hydroxy ketones are formed (equation II). 

Alternatively, as in the synthesis of l-methoxy-3,3-dimethyl-2-phenylcyclopropcnc (4), addition of tosylhydrazine to the a,/i-epoxy ketone 3 gave the. V-p-toluenesulfonate directly. 

Epoxidation is another important area which has been actively investigated on asymmetric phase transfer catalysis. Especially, the epoxidation of various (i.)-a,p-unsaturated ketones 68 has been investigated in detail utilizing the ammonium salts derived from cinchonine and cinchonidine, and highly enantioselective and diastereoselective epoxidation has now been attained. When 30 % aqueons H202 was utilized in the epoxidation of various a, 3-unsaturated ketones 68, use of the 4-iodobenzyl cin-choninium bromide 7 (R=I, X=Br) together with LiOH in Bu20 afforded the a,p-epoxy ketones 88 up to 92% ee,1641 as shown in Table 5. The O-substituted... 

P-Diketonesfrom %/i-epoxy ketones. 2 In the presence of this Pd(0) complex a,/ -epoxy ketones isomerize to /3-dikelones. An added ligand is usually necessary to avoid precipitation of palladium. The most satisfactory adjunct is l,2-bis(diphenyl-phosphino)ethane (dpe). The reaction is conducted in toluene at 80-140° for 10 100 hours. The isomerization is facile with strained epoxides it is sluggish with epoxides bearing an a-alkyl group. 

Photochemically induced ring cleavage reactions have also been reported in a,/i-epoxydiazomethyl ketones" and in a,/f-epoxy esters (glycidic esters).100 Two separate photoreactions are involved, however, in the rearrangement of phenyl epoxycinnamate (118) to the flavone (119), as shown in Scheme 7.101... 

A novel approach to the asymmetric synthesis of epoxides, allylic alcohols, a-amino ketones, and a-amino aldehydes from carbonyl compounds through a,/i-epoxy sulfoxides using the optically active p-tolylsulfmyl group to induce chirality./. Org. Chem. 1989, 54, 3130-3136. 

A catalytic method for the preparation of enantiomerically pure oc,/i-epoxy ketones as building blocks for organic synthesis is highly desirable. Unfortunately, the Julia-Colonna... 

Shibata, I., Yamasaki, H., Baba, A., Matsuda, H. Stereoselective synthesis of a,P-epoxy ketones by the Darzen s reaction with methyl N-ethyl-N-(tributylstannyl)carbamate. Syrr/etf 1990, 490-492. 

Eelix, D., Schreiber, J., Ohioff, G., Eschenmoser, A. Synthetic methods. 3. a,P-Epoxy ketone->alkynone fragmentation. I. Synthesis of exaltone and ( )-muscone from cyclododecanone. Helv. Chim. Acta 1971, 54, 2896-2912. 

Aryl ethyl ethers are deethylai exposure to microwaves in the pres of selectivity by the addition of eth Palladium halide complexed to haloarenes with powdered NaCN ii Olefiturtions. Vinylogation 1,3-dioxolan-2-ylmethyltriphen> Ipl feasible. Similarly, asymmetric Ej been induced by RbOH in the pte Oxidations and reductions. benzylamines to benzamides with aldehydes can be carried out in tolu Epoxidation of various alken phase-transfer conditions using so economical and environmentally I a,P-epoxy ketones are deoxj H,NC(=NH)SO,H under phase-tnu... 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Cleavage of epoxy ketonesThe reaction of benzoyl chloride and an a, /8-epoxy ketone proceeds in low yield and regiosclcctivity. However, addition of SnCI2 complexcd with (C(,Hs)2P results in high regiosclcctivity. In contrast, use of Bu2SnCl2/P(C,H )1 as catalyst results i.i cleavage at the opposite site. 

A novel interpretation of the chiroptical properties of cyclopropyl ketones has been proposed. " In addition to the two natural planes of symmetry of the carbonyl group, a third nodal surface is considered to be curved in a manner similar to that postulated last year for other carbonyl compounds, with its convex face towards oxygen. Cyclopropyl groups are then considered to obey a reversed octant rule i.e. one which reverses the signs of the original octant rule) with respect to the three boundary surfaces. O.r.d. and c.d. data are reported for a variety of pentacyclic triterpene derivatives with oxo-groups at C-3, C-12, and C-16, and for a series of compounds in the A-nor-2-oxo-series, including a,j8-epoxy-ketones and some lactones. ... 

Thermolysis of the epoxytosylhydrazones (495) provides a new synthetic route from a,i5-epoxy-ketones to cycloalk-4-yn-l-ones (496). i 2... 

Interestingly, we were intrigued by the ESI mass spectrum of the compound, as the observed base peak consisted of [M-S02+Na]+. This led us to explore a thermal retro-Diels-Alder reaction that could afford the desired enone 69. It is noteworthy that the chemistry of cyclic enol-sulfites would appear to be an under-explored area with a few references reporting their isolation being found [57]. At last, we were also able to prepare epoxy ketone 70 from 69 in three steps, albeit epoxidation did not take place unless the TES group was removed. Spartan models reaffirmed our initial conformational assessment of enone 69 and epoxy ketone 70, which contain sp3-hybridized C8a and s/r-hybridized C8b (p s e u d o-. v/r - h y b r i d i zed C8b for 70) at the AB-ring junction (Fig. 8.12) and displayed the desired twisted-boat conformation in A-ring. 

Reduction of an optically active epoxy ketone gives a chiral p-hydroxy ketone (equation I). 

A major pathway on irradiation of /I,y-epoxy ketones has been shown to involve a-cleavage. Thus, oxiran 120, on irradiation in benzene, is converted... 

E)-at,[l-Epoxy phenyl ketones. The ketones can be formed by an aldol-type reaction of a.a-dibromoalkyl phenyl ketones with aldehydes in the presence of SnF2 (equation I). 

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