Paterno

There are few examples of formation of simple azetidines from [2 + 2] fragments, although this type of approach is important for certain azetidine derivatives, e.g. azetidin-2-ones (see Section 5.09.3). Nitrogen analogues of the Paterno-Buchi route to oxetanes are rare an example involves the photoaddition of 3-ethoxyisoindolone (37) to the enol ether (38) (75JA7288, 72CC1144). 

PATERNO BUCHt 2+2 Cydoadditlon Photochemical 2+2 cyclization ol cartxinyia and oleflns to oxetanes... 

In general however the various possible reaction pathways give rise to formation of a mixture of products. The type I-cleavage reaction is only of limited synthetic importance, but rather an interfering side-reaction—e.g. with an attempted Paterno-Buchi reaction, or when an aldehyde or ketone is used as sensitizer in a [2 -I- l -cy do addition reaction. 

In addition to the intermolecular Paterno-Buchi reaction, the intramolecular variant has also been studied the latter allows for the construction of bicyclic structures in one step. For example the diketone 8 reacts quantitatively to the bicyclic ketone 9 ... 

Although the Paterno-Buchi reaction is of high synthetic potential, its use in organic synthesis is still not far developed. In recent years some promising applications in the synthesis of natural products have been reported. The scarce application in synthesis may be due to the non-selective formation of isomeric products that can be difficult to separate—e.g. 6 and 7—as well as to the formation of products by competitive side-reactions such as Norrish type-I- and type-II fragmentations. 

Scheme 2. The Paterno-Buchi reaction as a photochemical aldol equivalent.

Typical chemical reactions of photoexcited aldehydes and ketones are cleavage reactions, usually designated as Norrish Type I [equation (54)], II [equation (55)] and III [equation (56)], hydrogen abstraction [equation (57)] and cycloadditions, such as the Paterno-Buchi reaction [equation (58)]. Of these, Norrish Type II cleavage and the related... 

LORENZETTi s, PATERNO A, GERMANi D, ciANFARANi s and BRANCA F (2001) Phytoestrogens and lGF-1 in vitro regulation of bone resorption by osteoclasts. Ann Nutr Metab. 45 (5) 229. 

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... 

Some other examples of Paterno-Buchi reactions are given in Scheme 6.11. 

Scheme 1 UV-light induced formation of the two major photo lesions in DNA. T=T cyclobutane pyrimidine dimer. (6-4)-photo product (6-4)-lesion, formed after ring opening of an oxetane intermediate, which is the product of a Paterno-Buchi reaction...

In 1954 this reaction was more extensively investigated by Buchi,. Inman, and Lipinsky,(81) who confirmed the oxetane structure of the photoproduct. To credit their initial work on this interesting reaction, it commonly is referred to as the Paterno-Buchi reaction. 

This reaction was first discovered by Paterno and Chieffi in 1909.(90) These workers isolated a compound from the photolysis of benzophenone in... 

Taheri, S., Paterno, J Lin, L. Mignot, E. (2006). Narcolepsy and autoimmunity. In The Orexin/Hypocretin System Physiology and Pathophysiology, ed. S. Nishino T. Sakurai, Totowa, NJ Humana Press, pp. 341-6. 

One of the best-known and highly useful photochemical synthetic procedures is the Paterno-Biichi reaction [17]. This transformation has also been adapted as basic principle for domino processes by different research groups. Agosta and coworkers published a procedure by which tetrasubstituted furans such as 5-65 can be built up from 5-61 and 5-62 (Scheme 5.13) [18],... 

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... 

Cycloadditions of olefins and carbonyl compounds (Paterno-Biichi reaction)... 

The photoinduced [2 + 2] cycloaddition of carbonyl acceptors with electron-rich olefins leads to oxetanes (Paterno-Biichi reaction) with high regio- and stereoselectivities (equation 25). 

The photocycloaddition of an aldehyde or ketone with an olefin to yield an oxetane was reported by Paterno and Chieffi in 1909. 58> Contemporary studies on the synthetic utility and mechanistic features were initiated nearly 50 years later by Biichi et al. 59) Two review articles summarizing synthetic aspects of Paterno-Biichi reactions have been published 6.12)) and mechanistic studies have been reviewed several times. 6,38,60-62) The reaction involves the addition to olefin of a photo-excited carbonyl moiety. This circumstance makes it advantageous to review this reaction before a discussion of olefin-olefin additions, because the solution photochemistry of carbonyl compounds is probably better understood than any other aspect of organic photochemistry. Many of the reactions of carbonyl compounds have been elucidated during studies of the important phenomena of energy transfer and photosensitization. 63-65)... 

A clear division of Paterno-Biichi reactions into several distinct categories is possible on the basis of the type of reacting carbonyl compound (alkyl or aromatic), the excited state responsible for reaction (n—71 or Ti—n, singlet or triplet), and the type of olefin (electron deficient or electron-rich). Some examples of these reactions are given in Eqs. 7—11, where only the oxetane products are shown. 

A very complex group of observations and speculations has been presented in Section IV. It might almost seem illogical to apply a single theoretical approach to so diverse a set of reactions, but the utility of PMO theory for correlating the several aspects of Paterno-Buchi reactions has already been demonstrated. 38-39> The newer results to be presented below will help to confirm the idea that PMO theory gives a unified useful theoretical picture for the majority of [2+2] photocycloaddition reactions. First, however, the many approximations and postulates inherent in this work should be made clear. 

Oxetanes are the cycloadducts from a carbonyl compound and an olefin. This one step photochemical formation of a four membered ring heterocycle has been named the Paterno-Buchi reaction 489a> b). Oxetanes are important synthetic intermediates as they can fragment into the carbonyl-olefin pair by which they were not formed (a so termed carbonyl-olefin metathesis). Two examples of such oxetan cracking reactions are shown below in (4.76)490) and in (4.77)491) in this last example the oxetane was used as a precursor for the pheromone E-6-nonenol,... 

B. Paterno-Buchi Reactions Employing Conjugated Dienes. 297... 

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