Butadiyne photolysis

The photochemical hydration of one of the triple bonds of naphthyl-1,3-butadiynes is reported to yield naphthyl substituted ynones if the reaction is carried out in methanol rather than water then the primary products include (240) which result from addition of solvent or photoreduction. These compounds undergo secondary photochemistry and are found to photocyclise to the phenanthrenes (241). A similar reaction occurs for phenyl substituted 1,3-butadiynes. Photolysis of the phenyl iodonium ylid of dibenzoylmethane, i.e. (242), with terminal alkynes yields (243) which photocyclises in a similar manner to (240) to yield benzoyl-naphthols (244). °... 

Recently, detailed mechanistic studies have been made of the photolysis of l-aryl-4-(pentamethyldisilanyl)-l,3-butadiynes 96 in various solvents. Photolyses in the presence of methanol led to the isomeric products 97 and 98, derived from solvolytic ring opening of the initially formed silacyclopropene, 99, resulting in turn from 1,2-silyl migration48, while photolyses in acetone led to the products 100 and 101 arising from two-atom insertion into the three-membered ring49 (Scheme 14). 

In recent years interest in these materials has grown mainly for physical reasons. The layer perovskites are looked at as model compounds for the study of magnetic properties in two-dimensional systems (J2) and as models for the study of structural phase transitions in lipid bilayer-type arrays ( ). The use of layer perovskites as a matrix for organic solid state reactions represents a fairly new research topic. First experiments were carried out studying the photolysis of butadiyne (diacetylene) derivatives (li-ZSl) For a corresponding study of the butadiene derivatives the compounds listed in Table I were synthesized. 

Scheme 11-5 Formation of 1,3-butadiyne by the photolysis of didiazo compound 35 d.

Contrary to DPB, photolysis of l-phenyl-l,3-pentadiyne (PPD) [47] and l-phenyl-5,5-dimethyl-l,3-butadiyne(PDB) [39] with DMB yields only 1 1... 

Experiments with various quenchers were carried out to quench the triplet excited state of acetone selectively [95]. From these experiments it is confirmed that the silacyclopropene formed from the photolysis of l-aryl-4-(pentamethyl-disilanyl)-l,3-butadiynes reacts with acetone via the triplet excited state of the silacyclopropene, and the triplet energy of the silacyclopropene lies around 62-68 kcal/mol. 

The results of PdCl2(PPh3)2 catalyzed photolysis of l-phenyl-4-(penta-methyldisilanyl)-l,3-butadiyne with other alkynes support the involvement of this silylene complex [98]. 

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