Tetraphenyl cyclobutane

In the crystal of 1,4-dicinnamoylbenzene (1,4-DCB) (see Fig. 12), the distances between the intermolecular photoadductive carbons are 3.973 and 4.086 A for one cyclobutane ring, and 3.903 and 3.955 A for the other. The two topochemical pathways may occur competitively in a single crystal of 1,4-DCB at the initial stage of reaction. Then, both intramolecular photodimerization and intermolecular photopolymerization of the diolefinic mono-cyclobutane intermediate occur competitively to give tricyclic dimer 21,22,23,24-tetraphenyl-l,4,ll,14-tetraoxo-2(13),12(13-diethanol, [4.4] para-cyclophane or oligomers (Hasegawa et al., (1985). On photoirridation at room temperature the 1,4-DCB crystal gives >90% of the tricylic... 

Narasaka s chiral titanium catalyst, prepared from (Pr 0)2TiCl2 and a tartrate-derived (2R,3R)-l,l,4,4-tetraphenyl-2,3-0-(l-phenylethylidene)-l,2,3,4-butanetetrol, is utilized for the asymmetric [2+2] cycloaddition of A-acyl oxazolidinones to 1,2-propadienyl sulfides possessing a-substituents, which afford methylenecyclobutane derivatives with high enantiomeric purity. These chiral adducts are readily transformed to seven- and eight-membered carbocycles with chiral side chains by the ring-cleavage reaction and subsequent cationic cyclization of the chiral cyclobutane derivative [68] (Eq. 8A.44). 

The photolysis of l-trimethylsilylethynyl-l,l-diphenyltrimethyldisilane (63) is of considerable interest, because of a novel 1,2-disilacyclobutene is produced (107). When a benzene solution of 63 is photolyzed by irradiation with a low-pressure mercury lamp bearing a Vycor filter, yellow crystals of 1,1,2, 2-tetraphenyl-3,4-bis[bis(trimethylsilyl)methylene]-1,2-disila-cyclobutane (64) are formed. This can be readily isolated by evaporation of the solvent from the resulting mixture. The formation of 64 can be explained in terms of head-to-head dimerization of transiently formed sila-propadiene. 

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