De Mayo cycloaddition

OELEPINE Arrane synthesis 91 DE MAYO Cycloaddition 92 DEMJANOV Rearrangement 93 Demges 219 Dennstedt 64... 

A remarkable combination of a photochemical [2+2] cycloaddition with a retro-aldol reaction and cyclization is the so-called de Mayo reaction. Biichi and coworkers have used this method for the total synthesis of loganin (5-35). Thus, reac-... 

Following a report by Biichi and Ayer > on the photolysis of nitrobenzene in cyclohexene and 2-methyl-2-butene, a thorough study on nitrobenzene cycloaddition to olefines has been undertaken by de Mayo and co-workers 3 . ). Evidence was presented for the previously postulated ) formation of 1,3,2-dioxazolidines ... 

Fullerene, Cgo, undergoes photochemical 2 + 2-cycloaddition with /V,A-diethyl-4-methylpent-3-en-l-yn-l-amine to produce the stable Cgo-fused cyclobutenamine that is photo-oxidized to the dihydrofullerenone amide in high yield.15 The photochemical 2 + 2-cycloaddition of arylalkenes with Cgo has been shown to occur by a two-step mechanism involving the formation of a dipolar or diradical intermediate in the rate-determining step.16 The 2 + 2-photo-cycloaddition of cis- and irons-1 -(/j-methoxyphen-yl)-l-propene to C6o produces only trans-2 + 2-adduct. This is consistent with a two-step mechanism.17 The 2 + 2-photo-cycloaddition of cyclic 1,3-diones to Cgo results in the formation of two furanylfullerenes, one chiral and the other achiral. None of the expected De Mayo cyclooctane-1,3-dione addition products were formed.18... 

Berenjian, N., de Mayo, P., Sturgeon, M.-E., Sydnes, L.K., and Weedon, A.C. (1982) Biphasic photochemistry micelle solutions as media for photochemical cycloadditions of enones. Canadian Journal of Chemistry, 60, 425-436. 

The importance of the ethylene ketal described above with respect to stereocontrol of the de-Mayo reaction is emphasized by later published works of two other teams. Fetizon and co-workers obviously followed a similar concept and carried out photocycloaddition reactions with 96a in model studies (Scheme 23) (Si). As can be seen from retroaldol product 98, exclusive a attack of the cyclohexene has taken place. Thus, the relative stereochemistry of the BC ring connection is opposite to that of taxane. Totally comparable results were obtained by Berkowitz et al. in the course of cycloaddition reactions of cyclopentene, cyclohexene, or those of a cyclohexenone ketal to the camphor derivative 96b (.84). 

De Mayo reaction, [2+2]-cycloaddition of olefins and a,f-unsaturated carbonyl compounds... 

The product is formed via a [2+2]-cycloaddition de Mayo reaction) between cyclopentenone (2) and cyclobutene. The reaction is carried out under photochemical conditions, because the thermal process is symmetrically forbidden. A cw-cyclobutane is formed as is expected for de Mayo reactions with cyclopentanone (see Key Chemistry). 

Mixed cycloadditions, for example, between cyclopentenone and ethyl vinyl ether, have also been observed frequently (Schuster, 1989). As indicated in Scheme 25, attack of the n,K ) excited state of the enone on the olefin will give a triplet 1,4-biradical that ultimately yields cyclization and disproportionation products (Corey et al., 1964 De Mayo, 1971). The regio-... 

The synthetic achievement of the year in this field is certainly the synthesis of loganin penta-acetate (95) by Buchi et al. (Scheme 5). ° Using an extension of de Mayo s method for the synthesis of -diketones by photochemical cycloaddition of enolized /S-diketones to olefins, Buchi s group constructed the... 

II, 14, 15. Here intramolecular cycloadditions of enol esters, dioxinones and vinylogous esters and amides as /1-diketone equivalents will mainly be discussed. The examples shown belong to the de Mayo reaction in the broader sense as mentioned above. For more details see references 12 and 13. 

Intermolecular.— The control of regiospecificity in photocycloadditions remains a much sought after goal, de Mayo and Syndes have found that some control can be exercised on the reaction when the cycloadditions are carried out in micellar potassium dodecanoate (KDC). The ratios of products are sufficiently different (Table 1) from those obtained in non-polar solvents to merit further study of this... 

Some 1 -cycloadditions occur under irradiation with ultraviolet light. They are described in Chapter V (reactions by Biichi and Ayer and by Chariton and de Mayo). 

This reaction is related to the Diels-Alder Reaction, de Mayo Reaction, Patemo-BUchi Reaction, and Staudinger [2+2] Cycloaddition. 

In this sequence, most examples are due to the de Mayo ring expansion procedure, in which a cyclopentene undergoes a photochemical [2 + 2] cycloaddition with posterior retroaldol to cleave the intercycUc bond. 

In 1980, Baldwin developed a modification of the de Mayo reaction using dioxinone heterocycles as covalently locked enol tautomers of P-keto esters. Thus intermolecular cycloaddition of 2,2,6-trimethyl-1,3-dioxolenone 133 occurs in good yield using stoichiometric quantities of a variety of alkenes. For example, irradiation of 133 with tetramethylethylene yields the cyclobutane adduct 135 in 90% yield. This adduct is converted to cyclohexenone 138 in two steps. Controlled reduction of 135 with diisobutylaluminum hydride (DIBAL) gives keto aldehyde 137 (after spontaneous loss of acetone from hemiacetal 136 and retro-dXdo cyclobutanol fragmentation), which on exposure to acidic conditions affords cyclohexenone 138 in 76% yield. 

Wiesner carried out pioneering studies on the photocycloaddtion of vinylogous imides in the 1960s, and he first applied the intramolecular photochemical [2 + 2] enone-olefin cycloaddition reaction in natural product synthesis. In his landmark synthesis of 12-e/>i-lycopodine, compound 186 is irradiated to give a 70% yield of photoadduct 187. Protection of the ketone, epoxidation of the exocyclic double bond, and reduction of the epoxide give ketal alcohol 188. Deprotection of the ketal and spontaneous refro-aldol fragmentation lead to the diketone 190. Of note is that the bond cleaved in this retro-a do pathway (i.e., 189 to 190) is different from that of typical de Mayo reactions. Diketone 190 transforms to the tetracyclic alcohol 191 via aldol reaction, and this alcohol is converted to 12-e/7/-lycopodine in four steps. 

A system analogous to the taxanes has been prepared by using the intramolecular de Mayo reaction of vinylogous esters. Irradiation of the mixture of diastereomers 223 results in cycloaddition of one diastereomer to give adduct 225 and recovery of the other isomer 224. The tetrahydrofuran is oxidized with RUO4 to the lactone, which is saponified with concomitant cyclobutane cleavage to the diketo acid 227. 

The synthesis of loganin by BLichi et alP- illustrates the tactical use of the enone photoannelation technique, developed by de Mayo for synthesis of 6-diketones via photochemical cycloaddition of enolized /3 diketones to olefins. Thus, construction of the bicyclic iridoid nucleus is accomplished in a single photochemical operation followed by introduction of the C-7 methyl group and glucosidation to afford loganin penta-acetate. ... 

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