Photocycloaddition reactions alkenes

Three typical procedures will be presented (Sch. 19). The first represents one of the (only) two enone + alkene photocycloaddition reactions which have published as a procedure in Organic Synthesis [75], the second one is of... 

Arene-alkene photocycloaddition reactions have been reviewed in detail. This review includes a tabular survey, synthetic applications and exhaustive bibliography. Many of the reactions considered in this review were however performed to determine answers to mechanistic questions, therefore they are not necessarily optimized and chemical yields are not indicated. Tables 2 and 3 bring together, from the references cited in the review , those intermolecular photochemical meta cycloadditions which are principally synthetic methods. More concise general treatments of this reaction have since been published, as have other papers mainly concerned with its mechanistic aspects. """ ... 

Keese and coworkers have also used the intermolecular arene-alkene photocycloaddition reaction as a key step in another route to [5.5.5.5]fenestranes. Irradiation of 84 gave a mixture of products from which the desired adduct 85 could be isolated. Structure and stereochemistry of this tricyclic ester are supported both by earlier experience with the... 

Wender PA, Siggel L, Nuss JM (1989) Arene-alkene photocycloaddition reactions. Org Photochem 10 357-473... 

Wender, P. A., Siggel, L., and Nuss, J. M., Arene-alkene photocycloaddition reactions, Org. Photo-chem., 10, 357,1989. 

Photocycloaddition Reactions of Carbonyl Compounds and Alkenes. Photocycloaddition of ketones and aldehydes with alkenes can result in formation of four-membered cyclic ethers (oxetanes), a process often referred to as the Paterno-Buchi reaction.196... 

Scheme 6.11. Photocycloaddition Reactions of Carbonyl Compounds and Alkenes...

The synthetic applications 440) and mechanistic aspects 4411 of intermolecular photocycloaddition reactions of arenes to olefins have been reviewed recently. Intramolecular cycloadditions442a,b) have been studied in the context of the photochemical behaviour of bichromophoric molecules, as to investigate interchromophoric interactions in polyfunctional molecules. Three types of addition products can be formed in the photocycloaddition of benzene to an alkene (4.37)441. ... 

Both saturated or unsaturated thioimides and dithioimides behave like thioketones in their photocycloaddition reaction with alkenes (equation 129) and alkynes (equation 130)185. 

The same chromophores which undergo [2 + 2] photocyclodimerization (see Section 1.3.1.3.) obviously also undergo mixed [2 + 2] photocycloadditions to alkenes. Such reactions have been discussed in detail in Houben-Weyl, Vol. 4/5a, pp 360-412, pp 484-495, pp 620 624, and in Houben-Weyl, Vol. 4/5b, pp 912-947. 

Demonstration of the unique synthetic utility of the [2 + 2] photocycloaddition reaction of enones to alkenes and the success in controlling the stereoselectivity, to some extent, in the intermolecular additions (discussed above) prompted further studies and development of new synthetic applications in the intramolecular photoadditions during the last decade. In most cases that have been studied, the alkene was tethered to the cyclic enone by three carbon units or two carbons and one heteroatom. 

Ortho photocycloaddition reactions proceeding via excitation of the arene followed by intersystem crossing to the triplet state and reactions with the alkene have been reported by Wagner [93-103], Gilbert [104,105], Pete [106], and their co-workers. 

The possibility of the intermediacy of the triplet state of benzene itself has been discussed by Atkins et al. [108], Photoaddition of alkenes to arenes is often accompanied by the formation of dimers of the alkene, a reaction sensitized by triplet benzene. With methyl acrylate and methyl vinyl ketone, however, it was found that the ratio of ortho cycloadducts to alkene dimers increased with the concentration of benzene. Because the yield of T, benzene increases with benzene concentration, these results might indicate that ortho photocycloaddition of aery-... 

Diastereoselectivity in the (3 + 2) photocycloaddition of di-( )-menthyl, di-( )-8-phenylmenthyl, and di-( )-bomyl derivatives (398b-d) is largely dependent on the concavity of the auxiliary, steric bulk of the substituents of the alkenes, and reaction temperature [365] (Scheme 107). The highest de value was obtained when 8-phenylmenthyl ester 398c was employed, although the yield of the adducts was relatively low. The bomyl ester 398d showed poor diastereoselectivity. The effect of the chiral auxiliary seems to be reasonably explained in terms of the concavity of the auxiliary. When a-methylstyrene was used as the alkene, two stereoisomers of (3 + 2) adducts were obtained in lower yields than... 

A promising tool for controlling the regio- and stereoselectivity of photocycloaddition reaction (PCA) as well as the efficiency may be provided by assembling alkenes into a supramolecular structure with pre-organization of reactants such that the spatial arrangement of molecules would be favorable for the formation of only one cyclobutane isomer in a high yield. 

The Patemo-Biichi reaction is a photocycloaddition reaction of a n,ji carbonyl compound to an alkene in the ground state from either the Si or the rl i state. The reaction can occur through the initial C O bond formation or through a previous formation of the C—C bond. A frontier orbitals approach can be used to explain the formation of oxetanes. We can observe the HSOMO-LUMO interaction in which the half-occupied ji carbonyl orbital interacts with the unoccupied ji molecular orbital of an electron-deficient alkene, and a C,0-biradical is formed. The LSOMO-HOMO interaction in which the half-occupied n orbital of the carbonyl O atom interacts with the ji orbital of an electron-rich alkene, and a C,C-biradical is formed [13, 14]. 

Chappell, D. and Russell, A.T. (2006) From a-cedrene to crinipellin B and onward 25 years of the alkene-arene meta-photocycloaddition reaction in natural product synthesis. Organic tg Biomolecular Chemistry, 4 (24), 4409-4430. 

The photochemical cycloaddition of two different alkenes leads to multiply substituted cyclobutanes, and allows for a general access to this class of compounds. More specifically, ever since Ciamician observed the light-induced isomerization of carvone (1 —> 2) (Scheme 6.1) in 1908 [1], the inter- and intramolecular reaction between an a,(3-unsaturated carbonyl compound and an alkene has become the most intensively studied and most widely used class of [2 + 2]-photocycloaddition reactions [2-9]. 

The photocycloaddition chemistry of oc,P-unsaturated 8-lactones is similar to the chemistry of y-lactones. Complications arise as with cyclohexenones because anti-addition to the a,P-unsaturated double bond can occur, particularly in the intermolecular addition mode. Even if one product prevails, intermolecular [2 + 2]-photocycloaddition reactions are often sluggish. Despite the fact that alkene 92, for example, was employed in a twofold excess relative to dihydropyranone 91, the reaction delivered only 32% of the desired product 93 (43% based on recovered starting material Scheme 6.33). The relative product configuration, which was established by X-ray crystallography, came as a surprise because the lactone apparently... 

Termont, D., De Keukeleire, D., and Vandewalle, M. (1977) Regio- and stereoselectivity in [ 2 + 2] photocycloaddition reactions between cyclopent-2-enone and electron-rich alkenes. Journal of the Chemical Society, Perkin Transactions 1, 2349-2353. 

Bach, T. and Bergmann, H. (2000) Enantioselective intermolecular [2 + 2]-photocycloaddition reactions of alkenes... 

In contrast to photocycloaddition reactions of carbonyl compounds to electron-rich alkenes (which proceed with a low degree of stereoselectivity in the case of triplet excited carbonyls), reactions with electron-deficient alkenes, such as cyanoalkenes, are, although rather inefficient, but highly stereoselective [101]. Kinetic analysis showed that these reactions involve the... 

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