The photoisomerization of 2-methylenebicyclo[3.2.1]Octa-3,6-dienes; intramolecular allene cycloadditions

✍ Scribed by Harold Hart; Masayuki Kuzuya

• Publisher: Elsevier Science
• Year: 1974
• Tongue: French
• Weight: 172 KB
• Volume: 15
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)82591-0

✦ Synopsis

8icyclo[3.2.l]octa-3,6-dien-2-ones photoisomerize to ketenes (J + 2; ,4 + 0): When the ketene is hfghly substituted, as in the octamethyl derivative ,$' or is unusually reactive, as in the chloroketene :), intramolecular cycloaddition (GZs + n2a) competes successfully with attack by external nucleophiles, giving tetracyclic cyclobutanones (z and &).. && hu &S cl-bcl (ref 3) t D 5 D & To determine whether methylene analogs of these ketones would react similarly, we prepared and irradiated (ether, 45DW Hanovia lamp) trienes a. In each case the tetracyclic alkene & was obtained in >g5% yield. Since the trienes exhibit x,_,,~~ in the region 244-250 nm the photoisomerizations proceeded more rapidly using Vycor rather than Corex filtered light. Triene z5 gave &, whose structure was proved by independent synthesis from 3 and methyl-* enetriphenylphosphorane (rt, 3 days, s. 100%).