Molecular mechanics photocycloaddition

In addition to the [4+2] cycloaddition, intramolecular [2+2] photocycloaddition was also successfully used as a main procedure in the synthesis of (i)-ginkgolide B <00JA8453>. The studies on the model reactions and molecular mechanics calculation show that the stereochemistry of the substituents at C6 and C8 should influence severely the reaction diastereoselectivity. When syn-diastereomer 41 is subjected to irradiation the reaction gives a single diastereomer 42 in a quantitative yield since two substituents at C6 and C8 would be in pseudo-equatorial orientation in the chair-like transition state. 

The mechanisms of regioselective and stereoselective 2 -E 2-photocycloadditions have been extensively reviewed. The intramolecular 2 -E 2-photocycloaddition of 2-allyl-2-(l//)-naphthalenone (13) on the surface of silica produces all four cycloadducts (14)-(17) (Scheme 4). ° Molecular mechanics have been used to study the regio- and stereo-selectivity of the 2 -E 2-photocycloadditions in complexes containing crown ether styryl dyes and alkaline earth metal cations."... 

Molecular mechanics-valence bond dynamics have been used to study the model 4 + 4-photocycloadditions of butadiene with butadiene. The photoirradiation of t-butyl 9-anthroate and furan produces a mixture of 4 + 4-cycloadduct and 4 - - 4-cyclodimers. 

A series of 5-(2-methoxyphenyl)pent-l-enes (65), substituted at the a-, P-, or y- positions with either an OH or OSiMe3 group, undergo an intramolecular meta photocycloaddition reaction to give a product (66) having endo stereochemistry at the substituted carbon atom. The diastereoselectivity is a consequence of minimisation of steric interactions between the side chain substituent and the ortho-MQO group of the arene unit. A molecular mechanics study of the regio- and stereoselectivity of cation-dependent [2 + 2]-photo-... 

Scheme 4). ° Molecular mechanics have been used to study the regio- and stereo-selectivity of the 2 -E 2-photocycloadditions in complexes containing crown ether styryl dyes and alkaline earth metal cations."... 

The photoinduced polyaddition of l,l -(2,6-naphthalenedicarbonyl)diaziri-dine and 1,5-dihydroxynaphthalene occurs in high yield via the mechanism shown in Scheme 7. In the photocycloaddition of cis-cyclooctene to low molecular weight polystyrene, " the conversion is low. Poly-(4-methyl-4-trichloro-... 

Turro, N. J., Wriede, P. A. Molecular photochemistry. XXI. Photocycloaddition of acetone to 1-methoxy-1-butene. Comparison of singlet and triplet mechanisms and singlet and triplet biradical intermediates. J. Am. Chem. Soc. 1970, 92, 320-329. 

Poly(vinyl dnnamate) is the earliest synthetic photo-polymer Its molecular structure, the polyvinyl backbone with dnnamoyl side drains, was proposed with the expectation that the photocycloaddition of polymer-bound dnnamoyl groups would crosslink adjacent macromolecules. The practical aims of the inventors were realized, and the whole range of successful photopolymos has been developed from the ordinal idea However, the actual mechanism of oosslink formation in these systems remained unclarified untD recently. Repeated attonpts to identify cyclobutane derivatives in irradiated films of poly(vinyl dimamate) failed with traces of a-truxiUic acid detected in the hydrolyzed material only at the very early stage of irradiation. Schmidt... 

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