Cycloaddition of bis

Bis-o-quinodimethanes have also been used to functionalize [60]-fullerene by Diels Alder reaction. An example is the preparation of main-chain polymers with incorporated [60]-fullerene units [48] illustrated in Scheme 2.20. Cycloaddition of bis-diene 50 generated in situ from bis-sulfone 49 with [60]-fullerene leads to an oligomer mixture 51. Another type of functionalization is based on the... 

Diels-Alder Reaction in Unconventional Reaction Media Intramolecular Diels-Alder cycloadditions of bis-diene substrates [94]... 

Alkadienes and -trienes 1,3-Dipolar cycloaddition of bis(styryl) sul-fone ( , )-PhCH=CHS02CH=CHC6H4Me-4 with 4-MeOC6H4CH=NOH, in the presence of chloramine-T, gave a mixture of bis(isoxazolinyl) sulfone 49 and (styrylsulfonyl)isoxazoline 50 (220). 

The first metal-catalyzed [4 +2]-reaction of tethered dienes with 7r-systems was reported by Wender and Jenkins using alkynes initially as the two-carbon component.21 This study was based on the earlier observation by Wender and Ihle that in the [4 + 4]-cycloaddition of bis-dienes a competing side-reaction is the [4 + 2]-cycloaddition of the diene with a mono-ene portion of a second diene. The extension of this reaction to the synthesis of seven-membered rings by trapping the metallacycloheptadiene with CO, a formal [4 + 2 + l]-cycloaddition, has been shown in preliminary studies to be feasible. For example, tethered diene-yne 160 can be converted to cycloheptadienone 163 in an Rh(l)-catalyzed [4 + 2 + l]-reaction with CO, albeit the [4 + 2]- and [2 + 2 + l]-reaction products dominate (Equation (29)). The mechanistic scheme (Scheme 44) illustrates the possible metallacyclic intermediates leading to the observed products and provided the conceptual basis for the realization of three novel reaction types ([4 + 2], [2 + 2 + 1], and [4 + 2 + 1 ]).1... 

In conjunction with this, Jeong reported the cycloadditions of bis(allyl) and bis(homoallyl) acetals of alkynals leading to bicyclic lactols. Smaltz extended its utility to the synthesis of carbocyclic nucleoside by coupling with nucleophilic substitution of a 7r-allylic palladium complex (Equation (46)). ... 

Cycloaddition of bis(imidoyl chloride) 94 with the dianion of ethyl thioglycolate 93 allowed the synthesis of 2,3-diiminothietane 95 in 30% yield (Equation 30) <1999CC2439>. The thietane 95 was easily isolated by column chromatography. 

The activation barriers and reaction energies for the [2 + 2]-cycloaddition of bis-Cp vinylidene titanium complexes with different reagents with double and triple bonds have been theoretically investigated.1425... 

This method provides the basis for a general and efficient route to alkyl-substituted and heterofunctionalized bicyclo[6.4.0]dodecanes and to bicyclo[5.3.1]undecanes. In several model studies, the nickel-catalyzed intramolecular [4 + 4] cycloaddition of bis-dienes has been applied to the construction of diterpene systems, such as taxol (7), crispolide, and vulgarolide13 1S. Thus, in the case of taxol. both AB- and BC-ring fusion is achieved with high yield and high diastereoselectivity13. 

Scheme 3-10 Diels-Alder cycloaddition of bis-iodonium ethyn 30, with cyclopentadiene and furans and subsequent reaction of the adducts.

The isomeric p-lactone 60 bearing two trifluoromethyl groups at a-carbon was obtained by cycloaddition of bis(trifluoromethyl)ketene (61) to formaldehyde generated from trioxane (Scheme 2.28). " ... 

Rigby s studies on the synthesis of alkenylisocyanates fostered the preparation of a suitable substituted aryl enamide, which on photocyclization yielded the polysubstituted pentacyclic system. Key to the success of this process is the hydrogen bond between the phenolic OH and the carbonyl group, which restricts the rotation around the aryl-amide bond and directs the cyclization. Further functionalization allowed the total synthesis of pancratistatin (272) and narciclasine (68) (275) (Scheme 11). The [4-1-1] cycloaddition of bis(alkylthio)carbenes with vinyl isocyanates was the key process in a recent synthesis of (+)-mesembrine (92) 274). 

Whereas the preceding processes involving ring openings of cyclopropanes provide useful [3+2] entries to cyclopentanes, the use of simpler substrates in [3+2] cycloadditions is made possible by the development of reductive cycloaddition pathways. Such reactions were initially developed in the context of stoichiometric processes, where metallacycles were prepared by oxidative cyclizations of enones and alkynes, followed by either protonation or alkylation of the nickel 0-enolate functionality. Catalytic protocols involving various intramolecular combinations of 7t-systems include formal [3+2] reductive cycloadditions of bis-enones to form bicyclooctanols (Scheme 3-33), of enones with unsaturated acyl oxazolidinones to form triquinane derivatives, and of enals with alkynes to form bicyclooctenols. ... 

Although much less prevalent than the use of CO in lactone synthesis, direct incorporation of CO2 for the synthesis of lactones is advantageous due to lower toxicity while maintaining high atom efficiency. Louie and coworkers demonstrated that a formal [2 + 2 + 2] cycloaddition of bis-alkynes with CO2 yields pyrone derivatives under Ni(0) catalysis (Scheme 2.62) [117]. It is proposed that an initial cydometallation of one alkyne and CO2 yields a Ni(II) metallacycle, followed by insertion of the other alkyne and reductive elimination. Pd(0) has also demonstrated catalytic activity in carboxylations of methoxyallene [118] and 1,3-butadiene [119]. 

With these results in mind, we were attracted to two key points. The first was that building the complex bicyclic core system (20), with the four stereocenters as desired, could be achieved by diene-ene [2+2+1] cycloaddition of bis-diene (21) followed by reduction. The second attractive point was the diversification that could be achieved by cross metathesis at a late stage to get different analogs from the same bicyclic core (20). As a result, a retro-synthesis was conceived (Scheme 1) of isocarbacyclin methyl ester, or clinprost (3), having only nine steps.The first part of the synthesis, and most difficult part, was to generate bis-diene (21). 

The intramolecular radical cation 2 -I- 2-cycloadditions of bis(styrenes) were investigated by the DFT (U)B3LYP method. The key reaction pathway of the cycloaddition involves the formation of a five-membered ring intermediate in a stepwise manner. ... 

The 2 + 2 cycloaddition of bis-benzalacetone in the presence of UO2CI2 gives the truxinic derivative 7. The crystal structure determination of a complex formed between the unsaturated ketone and UO2CI2 showed the arrangement indicated in Scheme 16. It was argued that if the photodimerization occurred from this complex geometry the observed stereochemistry is the only one feasible [43]. 

The [2+2] cycloaddition of bis-trifluoromethylthioketene with ketenes proceeds similarly to give the four-membered ring cycloadducts 28. ... 

The enantioselective synthesis of C2-symmetric spirobipyridines were accomplished via the completely intramolecular double [2 + 2 + 2] cycloaddition of bis-diynenitriles by using [Rh(cod)2]BF4/axially chiral biaryl bisphosphine complexes as catalysts (Schemes 4.67 and 4.68) [58]. 

A palladium(0)/monophosphine complex is suitable for the synthesis of para-cyclophanes in the formal [2 - - 2 - - 2] cycloaddition of bis-enynes. 

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