Intermolecular addition reactions irradiation

INTERMOLECULAR ADDITION REACTIONS 2.1. Direct Irradiation With Tertiary Amines... 

Aoyama and co-workers have also investigated the intramolecular photoamination reactions of several tertiary (aminoal-kyl)styrenes. Irradiation of the (dibcnzylaminoalkyl)styrenes 28 and 29 results, respectively, in the formation of the pyrrolidine 30 and the piperidine 31 as mixtures of diastereomeric adducts. Irradiation of the (aminoalkyl)styrene 32 provides the bicyclic adduct 33 in good yield. Unlike the highly regioselective intramolecular addition of 22 and intermolecular addition reaction of stiibene with W,AI-dimethylisopropylamine (Scheme 3), the intramolecular reaction of the A/-methyl-Af-isopropylamine 34 yields a mixture of adducts 35 and 36 which result from N-methyl and Al-isopropyl hydrogen abstraction, respectively. 

Another solvent dependent intermolecular addition reaction involving phenylcyclopropane (64) as the electron donor was recently reported. Irradiation of N-methylphthahmide 42 in acetonitrile in the presence of 64 afforded a 1 1 mixture of isomeric spiro-tetrahydrofuranyl lactams 65 in 22% yield. An intramolecular version of this PET reaction has also been described."" When the photolysis was performed in methanol, solvent-incorporated addition to produce 66 took place (Scheme 23). 

Molander has also studied the Sml2-mediated double Barbier additions of alkyl dihalides to ketoesters.22,23 These impressive anionic-anionic, inter-molecular-intramolecular sequences require the use of Nil2 as an additive and irradiation with visible light and allow access to a range of bicyclic and tricyclic systems. The reactions proceed by reduction of the more reactive alkyl halide, intermolecular Barbier addition to the ketone, lactonisation and a second Barbier addition to the lactone carbonyl (Scheme 6.18).22... 

Hydroamination of olefins is also possible with gold catalysts. In this reaction, the attack comes Ifom a nitrogen nucleophile as a carbamate,a urea, an amide, or a sulfonamide. In the latter case, the reaction can be carried out intermolecularly. While the carbamates, ureas, and amides give only products of intramolecular anunations, the sulfonamides can perform the intermolecular addition. Only the addition of ureas (equation 146) takes place at room temperature, and in the rest of the additions heating is required. The catalysts of choice in all these reactions are cationic gold(I)-species stabilized by phosphines or NHC ligands. The reaction times have been reduced by the use of microwave irradiation. The mechanism of the hydroamination reaction has been studied in detail theoretically. ... 

The chiral molecular receptor (35) has been used to effect enantioselective cyclization of the enone (36). The complex of (36) and (35) undergoes energy transfer from the ketonic acceptor to (36) and results in its conversion into the cyclobutanes (37) and (38) in a total yield of 21%. Bach et aV have continued their investigations of enantioselective additions mediated by the chiral lactam hosts (39). The present reactions involve intra and intermolecular additions of quinolone systems (40) at -60°C in toluene as solvent. The irradiation affords the cycloadducts (41) and (42). As can be seen, the ee of the products is high and the chemical yields are also good. An extension of the work to intermolecular reactions of the quinolone (43) was also reported. The additions of the alkenes... 

The novel cage compounds (448, 449) are formed when duroquinone (450) is irradiated (Pyrex filter, benzene solution) in the presence of cyclohepta-triene. The reaction takes place via the intermediate (451), which subsequently undergoes intramolecular cyclization to yield (448) or intermolecular addition of duroquinone followed by intramolecular cyclization to afford the... 

The [Ir(ppy)2bpy] complex photo-catalyses inter- and intramolecular C-H functionalisation reactions of tertiary amines under the visible light irradiation. Oxygen behaves as a chemical switch, triggering different reaction pathways and leading to different products from the same starting material. In anaerobic conditions, the intermolecular addition of iV,iV-dimethyl-anilines to electron-deficient alkenes yields y-amino nitriles. Aerobic conditions, on the other hand, favour a radical addition/ cyclisation reaction, leading to tetrahydroquinoline derivatives. The intramolecular version of the radical addition produces unexpectedly indole-3-carboxaldehyde derivatives. ... 

In addition to these intramolecular processes, n- n excited ketones can undergo typical intermolecular radical reactions. Thus irradiation of benzophenone (49) in isopropanol (50) gives the pinacol (53) and acetone as follows ... 

In addition, microwave irradiation accelerated this transformation by at least 8-fold. Additives, in particular a quinolinium salt, were found to facilitate the intramolecular reaction of diynes that would not otherwise macrocyclize, apparently through an intermolecular noncovalent 7t-cation/arene inter-action. " It is noteworthy that RCM also can be assisted with such additives. These studies have positioned the Glaser-Hay reaction for investigation in the preparation of macrocycles from more complex substrates. 

Similar intermolecular alkylation reactions can occur by irradiation of primary or secondary alcohols in the presence of sensitizers. The resulting a-hydroxyalkyl radicals [R2(HO)C] have been shown to add to a range of double bond acceptors. Recent examples, which lead to the formation of new carbon-carbon bonds, include addition to maleimides," a dihydropyrrole, and a 2,2-difluorovinyl carbamate. ... 

Irradiation of the cyclohexenone 32 with the tertiary a-silylamine EtjNCHjSiMe, affords two adducts 32a and 32b in a product ratio that is solvent dependent (Scheme 20). In acetonitrile solution, the formation of 32a as major product can be attributed to selective a-CH deprotonation adjacent to the silyl substituent, whereas the formation of 32b as the major product in methanol solution can be attributed to nucleophihc displacement of the silyl group followed by addition of the radical EtNCHj to either the neutral enone or its anion radical. Intramolecular analogs of this reaction have also been studied for substrates 33 and 34 and display highly selective a-CH deprotonation adjacent to the silyl substituent in acetonitrile solution to yield 33a and 34a and desdylation in methanol solution to yield 33b and 34b (Scheme 21). Intramolecular addition can also compete with trans,cis isomerization of acychc enones, whereas intermolecular addition is too slow to do so. " ... 

Bazureau described a tandem conjugate addition-intermolecular hetero-Diels-Al-der reaction of perimidine derivatives under solvent-free conditions with focused microwave irradiation [77]. The main feature of this reaction was attainment of complete addition in less than 8 min. When the reaction mixture was heated in an oil bath set at the same temperature for the same time the results were analogous (Scheme 9.27). 

As noted above, formation of a furan [4 + 3]-cycloadduct during irradiation of a 4-pyrone was advanced as evidence for the zwitterionic intermediate. This process can be moderately efficient (equation 4)68, and can be envisioned as an approach to substituted cyclooctanoids. Besides the formation of three new carbon-carbon bonds, an additional attractive feature is the complete diastereoselectivity, arising from a compact [4 + 3]-cycloaddition transition state with approach from the face opposite the epoxide. However, the generality of the intermolecular reaction is limited, as competing [2 + 21-photodimerization, solvent trapping and rearrangement often predominate58. 

There are a number of possible explanations for the formation of more than one photodimer. First, due care is not always taken to ensure that the solid sample that is irradiated is crystallographically pure. Indeed, it is not at all simple to establish that all the crystals of the sample that will be exposed to light are of the same structure as the single crystal that was used for analysis of structure. A further possible cause is that there are two or more symmetry-independent molecules in the asymmetric unit then each will have a different environment and can, in principle, have contacts with neighbors that are suited to formation of different, topochemical, photodimers. This is illustrated by 61, which contrasts with monomers 62 to 65, which pack with only one molecule per asymmetric unit. Similarly, in monomers containing more than one olefinic bond there may be two or more intermolecular contacts that can lead to different, topochemical, dimers. Finally, any disorder in the crystal, for example due to defective structure or molecular-orientational disorder, can lead to formation of nontopochemical products in addition to the topochemical ones formed in the ordered phase. This would be true, too, in those cases where there is reaction in the liquid phase formed, for example, by local melting. 

The most widely exploited photochemical cycloadditions involve irradiation of dienes in which the two double bonds are fairly close and result in formation of polycyclic cage compounds. Some examples are given in Scheme 6.7. Copper(I) triflate facilitates these intramolecular additions, as was the case for intermolecular reactions. 

Analysis of the product distributions arising from both sensitized and non-sensitized irradiation of 2-allyloxyphenyldiazo species (8) showed that the C—H insertion product and much of the cyclopropanation arise from the triplet carbene.16 For the singlet carbene, intermolecular 0—H insertion with methanol is about 50 tunes faster than intramolecular addition to the double bond, hi this system, intramolecular reactions and intersystem crossing of the triplet carbene proceed at similar rates, hi the closely related indanyl system (9), the smaller RCR angle stabilizes the singlet state relative to the triplet and the intramolecular reactivity is dominated by the singlet state.17... 

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