Efficient Synthesis and Theoretical Study of Siloxy-Benzocyclooctenes: 7,8-Bis-trimethylsilanyloxy-5,6,9,10-tetrahydro-benzocyclooctene and 6,9-Dimethyl-7,8-bis-trimethylsilanyloxy-5,6,9,10-tetrahydro-benzocyclooctene-6,9-dicarboxylic Acid Diethyl Ester

2-[2-(2,2-Bis-ethoxycarbonyl-ethyl)-benzyl]malonic acid diethyl ester 2, 3-[2-(2-ethoxycarbonyl-ethyl)-phenyl]-propionic acid ethyl ester 3, 2-[2-(2,2-bis-ethoxycarbonyl-propyl)-benzyl]-2-methyl-malonic acid diethyl ester 4, 7,8-bis-trimethylsilanyloxy-5,6,9,10-tetrahydro-benzocyclooctene 5, and 6,9-dimethyl-7,8-bis-trimethylsilanyloxy-5,6,9,10-tetrahydro-benzocyclooctene-6,9-dicarboxylic acid diethyl ester 6 have been synthesised for study of their spectroscopic and structural features. The synthetic method involved is monoalkylation of malonic acid diethyl ester and 2-methyl-malonic acid diethyl ester with 1,2-bis-bromomethyl-benzene in DMSO, and yields esters 2 and 4, respectively. The decarboxylation of 2 by DMSO/LiCl in the presence of a very small amount of water yields diester 3. Compounds 3 and 4 undergo acyloin condensation to give siloxy-benzocyclooctenes 5 and 6, respectively. The calculated structures and parameters of bis-siloxy-benzocyclooctene 6 show the reason why cyclization of 4 was independent of the quantity of reagents used.