Photocyclization 2+2 photocycloaddition

There has been considerable interest in various photocycloaddition reactions over the last years which not only broadened the number of useful photochemical applications but also revealed further mechanistic insight into these reactions [76,77]. Among these reactions, reports focusing on either the [2 -h 2] or the [4 -I- 2] cycloaddition, are numerous. Also the efforts toward the enantiodifferentiating photosensitization in photocyclization reactions have to be mentioned [78],... 

A. Gilhert, in W. M. Horspocl (ed.). Synthetic Organic Photochemistry, Plenum 11984). Photoaddition, photocycloaddition and photocyclization processes of aromatic compounds are all covered in this account of synthetic aspects of aromatic photochemistry. 

Kohmoto et al. examined the photocyclization of /V-cinnamoyl- l -naph-thamides (274a-f) in benzene solution and in the solid state [295] (Scheme 77). Intramolecular (2tt + 2tt) and (2tt + 4tt) photocycloaddition of styryl group to the naphthalene ring was observed in benzene solution, whereas 275a-c were also obtained in the solid state. 

D. Photocycloaddition and Photocyclization Within Nation Membranes, Zeolites, and Vesicles... 

Stereoselectivity of Photocycloadditions and Photocyclizations Axel G. Griesbeck and Maren Fiege... 

CONTENTS Preface, Mark Lautens. Photocyclization and Photocycloaddition Reactions of 4- and 2-Pyrones, Frederick G. West. Intramolecular [4+3] Cycloaddition Reactions, Michael Harmata. Lewis Acid Catalyzed [2+2] Cycloaddition Reactions of Vinyl Sulfides and Their Analogues Catalytic Asymmetric [2+2] Cycloaddition Reactions, Koichi Narasaka and Yujiro Hayashi. Vinylboranes as Diels-Alder Dienophiles, Daniel A. Singleton. Preparation and Exo-Selective [4+2] Cycloaddition Reactions of Cobaloxime-Substituted 1,3-Dienes, P... 

The efficiency of these chiral host compounds has been shown in highly enantioselective photocyclization and photocycloaddition reactions of prochiral lactams. These substrates, for example 2-quinolone derivatives, are expected to coordinate to lactam 44 with its NH-group as the hydrogen donor and the carbonyl group as the hydrogen acceptor, as depicted in Scheme 15. In this complex, any... 

The Patemo-Buchi reaction is the photocycloaddition of an alkene with an aldehyde or ketone to form oxetanes. This transformation has been shown to proceed through a biradical intermediate, and up to three new stereocenters can be formed as a result of this reaction. A general mechanism for the reaction between an aldehyde and a chiral enol silyl ether is shown in Eq. (13.7) [18]. Allylic 1,3-strain is cited as the control element in reactions of this type, and diastereomeric ratios of >95 5 are reported for products 30 containing four contiguous stereocenters. Examples of photocyclizations of amino acid derivatives proceeding through biradical intermediates have been repotted [19]. 

Toda et al. [73] described photocyclization in the solid state, using various chiral lattices (e.g., 23) as the host for the [2+2] photocycloaddition of an enone teth-... 

---