Intramolecular photocycloaddition synthesis

Mizuno, K., Kagano, H., and Otsuji, Y. (1983) Regio- and stereoselective intramolecular photocycloaddition synthesis of macrocyclic 2,co-dioxabicyclo [n. 2.0] ring system. Tetrahedron Letters, 24, 3849-3850. 

A novel entry to decahydrocyclopentacyclooctene derivatives via the intramolecular photocycloaddition of fused a,/3-unsaturated y-lactones has been developed (80CC1011). Irradiation of the butenolide (153) in acetone solution gave both the fused and bridged photoadducts (154) and (155) (2-3 1). The major adduct was hydrolyzed, oxidized and esterified to afford (156). Reductive cleavage of the unsaturated keto ester (156) with lithium in ammonia afforded a five-component mixture of a,/3- and /3,y-unsaturated esters. Equilibration with 0.1M sodium methoxide in methanol converted the mixture into a single a,j8-unsaturated ester (157 Scheme 34). This annelative two-carbon ring expansion method may find application in the synthesis of ophiobolin and ceroplastol sesterterpenes. 

General and stereoselective synthesis of spiroethers and less thermodynamically stable spiroketals have recently been developed by Hadded and coworkers129,130. The key step is the intramolecular photocycloaddition of chiral dioxinones of type 305 to dihydropyrones. Subsequent fragmentation of the produced four-membered ring provides, after oxidative enlargement of the cyclic ketone, the thermodynamically less stable spiroketal 310 (R = H) as was demonstrated on photoproduct 308 (Scheme 66). 

Kaneko, C., Suzuki, T., Sato, M., and Naito, T. (1987) Cydoadditions in syntheses. XXXII. intramolecular photocycloaddition of 4-(w-alkenyloxy) quinolin-2(lH)-one synthesis of 2-substituted cydobuta[c]quinolin-3 (4H)-ones. Chemical el Pharmaceutical Bulletin, 35, 112-123. 

An elegant application of this photocycloaddition in the field of triquinane synthesis has been reported by Reddy and Rawal [160]. The initially formed oxetane 163, formed from the Diels-Alder adduct 162, is easily cleaved reductively (by use of LiDBB = lithium di-/er -butyl-biphenylide) to give 164. This approach was also used for the construction of structurally diverse di- and (propellane-type as well as linear or angular anellated) triquinanes [161]. The classic linear triquinane hirsutene is also available via this route [162]. Star-like molecules like the tiene 167 are available via a sequence of intramolecular photocycloaddition (from the 1,3-cyclohexadiene/acylallene adduct 165) and oxetane (166) ring-opening (Sch. 58) [163]. Further examples of intramolecular... 

Kohmoto et al. reported a fine example of absolute asymmetric synthesis involving the intramolecular [4 4- 4] photocycloaddition of 9-anthryl-Af-(naph-thylcarbonyl)carboxamide derivatives 42a-g in the solid state (Scheme 20) [26]. Out of seven carboxamides examined, 42a, 42e7 rid 42g showed intramolecular photocycloaddition in the solid state to give the [4 + 4] cycloadducts 43a, 43e, and 43g in almost quantitative yields after complete conversion and 42f gave 43f in 9% yield (Table 9). However, 42b, 42c, and 42d were unreactive. The crystals... 

A number of model esters related to lac resin have been prepared. These esters have the basic cedrane skeleton (149) or the C-2 epimeric structure. In an approach to the synthesis of cedrene (152), the intramolecular photocycloaddition of the dienone (150) was carried out at low temperature. A major tricyclic compound (151) was obtained and its structure was verified by X-ray analysis of its anisylidene derivative. Further work is required to bring about the rearrangement of a derivative of (151) to give cedrene. Further details on the hydroxylation (with O3) and chlorination (with PhICl2) of cedrol, patchoulol, and their derivatives have been presented. The results of this study are in keeping with those obtained previously. 

A recent synthesis of 3-substituted furan derivatives illustrates an important application of the furan-carbonyl photocycloaddition. Zamojski has reported the rearomatization of oxetane (115) in the presence of p-toluenesulfonic acid to 3-furylmethanol derivative (116). Synthesis of (117), itself a substrate for the intramolecular photocycloaddition reaction (Section 2.4.6), involved a similar rearomatization process (PPTS/CHjClj) and capitalized upon the chemoselectivity observed in the ketone-furan photocycloaddition. Similarly, a synthesis of perillaketone (118) by Kawanisi involved irradiation of a carbonyl compound and furan. A complication in the rearomatization is that acid also catalyzes the reversion of the photoadduct to starting materials to circumvent this problem the photoreaction was run in the presence of acid, so that rearomatization would occur in situ and the products of competitive reversion would promptly recombine. 

The tricyclic ketone (17), a fragrant and volatile key compound of the zizaene (19) synthesis, results from a fragmentation of the tetracyclic mesylate (16). This skeleton has also bron formed by intramolecular photocycloaddition of the easily accessible enol acetate (18). Obviously, the ting strain of (16) is a strong driving force (Scheme 10). 

The sequence of intramolecular photocycloaddition-cyclobutane fragmentation has been used by Crimmins in an excellent manner for the synthesis of pentalenenes and the even more sophisticated lauren-l-ene (27). The latter synthesis was accomplished in 27 steps from cyclopentenone U66). One of the key steps is the reductive cleavage of the tetracyclic cyclobutane (167), followed by hydrogenation of the resulting P,7-unsaturated ester to give keto ester (168 Scheme 57). 

An approach to the synthesis of homosecoprismanes has also been developed using intramolecular photocycloaddition reactions of the enediones (252) and (253). The irradiation of these in benzene affords the cycloadducts (254) and (255), respectively in 80-90% yield. ... 

Functionalized substituted cyclopentanes and spirocyclopentanes were easily accessed by intramolecular photocycloaddition of dihydrofuran based dienes catalyzed by Cu(i) salts. Thus, tricyclic compound 39 was synthesized in 60% yield starting from 38 (Scheme 2.22). Notably, 39 can be easily transformed upon treatment with triflic acid into substituted cyclopentanones, which are important building blocks in the total synthesis of natural products. ... 

The intramolecular photocycloaddition of the alkenyltropone (55) is reported to yield (56) which is then used as the starting material for a synthesis of the natural product dactylol, (57)... 

Strained cage compounds can be made by intramolecular photocycloaddition of properly designed ene/enone substrates. In an interesting example from J. R. Scheffer, a ben-zoquinone derived Diels-Alder product is regioselectively transformed into a (halO cage compound. This is a more complicated version of the classical intramolecular photochemical cyclization reactions of benzoquinone derivatives (for example see B. Pandey s cage synthesis from a naphthoquinone-cyclopentadiene in Chapter 3). 

Although the [2 + 2] photocycloaddition is preferably prevented in the synthesis of PAHs, it has been proven to be a very feasible approach in the selective synthesis of syn-[2.2]cyclophanes [86,87]. Topological reaction control in solution has been achieved for a multistep intramolecular [2 + 2] cycloaddition reaction in the photochemical formation of [n]-ladderanes from pseudo-gem-bis(polyene) substituted [2.2]paracyclophanes [88]. The probably most well-known example of an intramolecular photocycloaddition process is one of the... 

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