Cycloaddition spiro -2 ,4 -diones

Reaction of thiochroman-3,4-diones with NaBH4 affords a mixture of the as- and trans- 3,4-diols and two keto alcohols result from reaction with MeMgl. Attempts to separate the latter mixture by preferential dehydration of the thiochroman-4-ol gave unchanged 3-hydroxythiochromanA-one, but no 4-methylenethiochroman-3-one was detected. Instead, a spiro-linked adduct arising from a hetero Diels-Alder cycloaddition between two molecules of the expected dehydration product was isolated (Scheme 102) <1994T7865>. 

Photoinduced [2+2] cycloadditions of lH-l-acetylindole-2,3-dione (13) with alkenes gave spiro-oxetanes 14 in moderate to high yields, displaying the typical triplet n-n reactivity of acetylisatin (Sch. 3) [18]. The regioselectivity and diastereoselectivity of these reactions depends on the... 

The cycloaddition of 4-methyl-3//-l,2,4-triazole-3,5(4/f)-dione to spiro[fluorenyl-l,3,5-cyclo-heptatriene] at — 10°C gives the norcaradiene-type cycloadduct, monitored by NMR spectroscopy, which by warming at room temperature is converted to an isomeric triazolidinedione, whose structure is confirmed by X-ray analysis22. 

On reaction of spiro[bicyclo[2.1.0]pentane-5,l -cyclopropane] with 4-phenyl-4/f-l,2,4-triazole-3,5-dione the bridge was cleaved and cycloaddition to the N-N double bond took place giving 4-phenyl-2,4,6-triazaspiro[cyclopropane-l,10 -tricyclo[5.2.1.0 ]decane-3, 5 -dione] in quantitative yield. 

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

A detailed account of condensation reactions used in heterocyclic chemistry can be found in Section 8.2.6, in Chapter 10 [97], and, for cycloaddition reactions, in Chapter 11 [98]. A previously unknown class of compounds, spiro[3H-indole-3,2 -[41-f] pyrido[3,2-e]-l,3-thiazine]-2,4 (ll-f) diones, can be synthesized by reaction of in situ-generated 3-indolylimine with 2-mercaptonicotinic acid under the action of MW in the absence of solvent. Both neat reactions and reactions on solid supports such as silica gel, alumina etc., effectively promote the reaction whereas reactions under thermal heating conditions failed to proceed (Scheme 8.31) [99]. 

The ethylenic double bond in cyclobutene-l,2-diones was unreactive in attempted cycloadditions with mesitonitrile oxide. Addition took place preferentially at the carbonyl groups to spiro-dioxazoles. The periselectivity has been disccused in terms of frontier MO interactions. 

Singh, V. Raju, B.N.S, p4S + p2S cycloaddition of spiro[4, ] cyclic 1,3-dienes with quinones in homogeneous and aqueous micellar media synthesis of novel polycyclic cage diones, Ind J. Chem., 1996,35B, 303-11. 

Photoinduced reactions of cyclic a-diketones with different alkenes takes place via [2 + 2], [4 + 2] or [4 + 4] photocycloaddition pathways. Photoaddition of electron deficient silyl ketene acetals to 2-, 3- and 4-acetylpyridine generates oxetanes as major products. The reaction is favoured in non polar solvents. The photoreaction between silyl enol ethers and henzil affords [2 + 2] cycloaddition products, while in the case of 9,10-phenanthrenequinone [4 + 2] cycloacidition predominates. Photocycloaddition of p-henzoquinones to hicyclopropylidene affords spirooxetanes (21) as the primacy products further irradiation leads to rearranged spiro[4.5]deca-6,9-diene-2,8-diones. With 9,10-anthraqui-none, in addition to the spirooxetane, a spiro[indan-l,l -phthalan]-3 -one is also obtained. ... 

There are several examples in literature on cycloaddition of alkenes to azomethine ylides, generated in situ by decarboxylative condensation of isatins with an a-amino acid, sarcosine (MeNHCH2C02H), for architecture of pyrrolidine ring in spiro-pyrrolidine-oxindoles [55]. The cycloaddition of ylide 62 from N-methylisatin 58 and sarcosine to 3,4-diphenylcyclobutene-l,2-dione 63 proceeded smoothly to afford the product 64 (Scheme 20) [56]. 

V. Nair, K.C. Sheela, N.R Rath, Dipolar cycloaddition reactions of isatin derived azomethine yKde with 3,4-diphenylcyclobutene-l,2-dione synthesis of novel spiro[oxindole-3,2-pyrrolidine] derivatives, Chem. Lett. (2000) 980-981. 

Perumal et al. prepared a library of l-methyl-4-arylpyrrolo-(spiro[2.2 ]indan-l, 3 -dione)-spiro[3.3"]-l"-methyl/ benzyl-5 -(arylmethylidene)piperidin-4"-ones 185 and l-methyl-4-arylpyrrolo-(spiro[2.11 ]-llH-indeno[l,2-b] quinoxaline)-spiro[3.3 ]-l"-methyl/benzyl-5 -(arylmethylidene)piperidin-4 -ones 186 in good yield (Scheme 109) via 1,3-dipolar cycloaddition of azomethine ylide in the IL [BMIM][Br]. The reactions were realized by heating an equimolar mixture of the reactants in IL in an oil bath at 100 °C for 1-2 h. After completion of the reaction, the products were isolated and purified by simple recrystallization from ethanol, while the IL could be recovered and reused further without appreciable decrease in the catalytic activity [289]. 

In Section 5.3.1, an example of the typical reactivity of a-oxo-ketenes as 1-oxa-dienes in inverse demand oxa-Diels-Alder reactions was presented. It was recently discovered that in the presence of 1-aza-dienes, a-oxo-ketenes can also react as dienophiles in microwave-assisted aza-Diels-Alder cycloadditions, and this reactivity was exploited for the diastereoselective synthesis of a series of a-spiro-8-lactams (Scheme 5.4). Paralleling the three-component approach presented in Section 5.3.1, the microwave irradiation at 140 °C for 15 minutes of a 1 1 1 mixture of the 5,5-dimethyl-2-diazocyclohexan-l,3-dione 1, benzyl-amine, and cinnamaldehyde furnished the a-spiro-8-lactam... 

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