Zur Darstellung und Stereochemie von Pentatetraenen

Abstract

On the Preparation and Stereochemistry of PentatetraenesThe synthesis of five new aromatic, mixed aromatic-aliphatic and aliphatic substituted pentatetraenes is described. The pentatctraenes 1 a and b are prepared by Kuhn's mcthod 'I. According to the expected C,,-symmetry of the pentatetraene chain the benzylic protons of 1 b should be diastereotopic, but shift differences of these protons in the 'H n. m. r. spectrum cannot be resolved even at 360 MHz. Reactions of the butatrienes 2a, b and 15 with dichlorocarbene as prepared by Makosza" yield the monoaddition products 3a, b and 16, from which the pentatetraenes 4a, b and I8 are formed with inethyllithiurn. With excess of dichlorocarbenc the diaddition products 6 and 14 are obtained. The allene-like geometry of the pentatetraene 4 b is shown by 'H n. m. r.').Some reactions of the pentatetraencs and a simple method for the preparation of 2-butyne-l,4-diols are rcported.

Synthesis and properties of long [n]cumulenes (n≥ 5)

“…Bildstein's approach is conceptually similar to that reported earlier by Nakagawa and coworkers, 110 in which two different endgroups have been introduced in order to explore optical activity and racemization of [4]cumulenes. Another possibility of the formation of tetraaryl [4]cumulenes has first been described by Kuhn 111 and then Karich and Jochims 112 and relies on the intermediate formation of dibromo-1,4-pentadienes from the appropriate unsubstituted dienes (Scheme 5). The diene is then converted to the [4]cumulene in good yield through base-induced elimination.…”

“…[3]Cumulenes can be converted to [4]cumulenes via addition of dichlorocarbene to a [3]cumulene, followed by rearrangement or reductive elimination, depending on the structure of Their route also provides rare examples of mixed dialkyl/diaryl endcapped [4]cumulenes. 112 Irngartinger and Götzmann have developed a slightly modified version of this general protocol to synthesize [4]Cy, using Zn in the final reductive elimination step (Scheme 6). 113 [4]Cumulenes can be obtained via carbene trapping as demonstrated by le Noble and coworkers (Scheme 7).…”

“…Another possibility of the formation of tetraaryl [4]cumulenes has first been described by Kuhn 111 and then Karich and Jochims 112 and relies on the intermediate formation of dibromo-1,4-pentadienes from the appropriate unsubstituted dienes (Scheme 5). The diene is then converted to the [4]cumulene in good yield through base-induced elimination.…”

“…Their route also provides rare examples of mixed dialkyl/diaryl endcapped [4]cumulenes. 112 Irngartinger and Go ¨tzmann have developed a slightly modified version of this general protocol to synthesize [4]Cy, using Zn in the final reductive elimination step (Scheme 6). 113 [4]Cumulenes can be obtained via carbene trapping as demonstrated by le Noble and coworkers (Scheme 7).…”

Synthesis and study of novel silicon-based unsaturated polymers

“…After purification on a silica-gel column Ohexanes as eluents), compound 26 was obtained as colorless crystals, m.p. [115][116][117]in 33% isolated yield. GCMS m/z 483(8), 482 (22), 480 (66, M), 467 (18), 466 28 17, 315 (34), 314 (100, M), 301 (12), 300 20, 299 (64), 225 (14), 211 (16), 187 20 Synthesis of 1.3-bisfchlorodimethylsilylV1.3-bis(trimethvlsiIyn-1.2-diene (32') and…”