Generation of alpha-phosphonovinyl radicals and development of a new route to highly functionalized vinylphosphonates and vinylphosphonate-incorporated carbocyclic or heterocyclic compounds via a radical trapping sequence.
The first direct generation of synthetically useful alpha-phosphonovinyl radicals was achieved by treatment of alpha-phosphonovinyl halides with a tributyltin radical. The alpha-phosphonovinyl radicals 2a-d were trapped with electron-rich olefins and an electron-deficient olefin to produce alpha-functionalized vinylphosphonates 3a-f in 16-55% yields. The alpha-phosphonovinyl radicals 7e-g containing the YCH2CH=CH2 (Y = O, CH2, S) substituent at the beta-position afforded mixtures of 5-exo and 6-endo cyclization products, 5e-g and 6e-g, in good yields. The 5-exo/6-endo product ratios increase in the following order of the beta-substituent: OCH2CH=CH2 > CH2CH2CH=CH2 > SCH2CH=CH2. The effects of the beta-substituents upon the cyclization reaction were discussed. Radical cyclization of alpha-phosphonovinyl radicals bearing functional groups such as geranyloxy, geranylthio, and (2-cyclohexen-1-yl)thio groups at the beta-position afforded 5-exo, 5-exo and 6-endo, and cis-fused-5,6-ring cyclization products incorporating an alpha,beta-unsaturated phosphonate unit within the ring, respectively, in good yields. The alpha-phosphonovinyl radical 20 underwent tandem radical cyclization-radical cyclization to produce a mixture of two isomeric bicyclo[4.3.0]nonenes including a vinylphosphonate moiety in high yield.
Ageno
Takafumi
T
Department of Applied Chemistry, Kyushu Institute of Technology, Sensui-cho, Tobata, Kitakyushu, 804-8550, Japan.
Okauchi
Tatsuo
T
Minami
Toru
T
Ishida
Masaru
M
D000475:Alkenes / Q000737:chemistry; D003500:Cyclization; D005609:Free Radicals / Q000737:chemistry*; D006219:Halogens / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D006844:Hydrocarbons, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D063065:Organophosphonates / Q000737:chemistry*; D013816:Thermodynamics; D014220:Trialkyltin Compounds / Q000737:chemistry; D014753:Vinyl Compounds / Q000737:chemistry*
D000475:Alkenes; D005609:Free Radicals; D006219:Halogens; D006571:Heterocyclic Compounds; D006844:Hydrocarbons, Cyclic; D063065:Organophosphonates; D014220:Trialkyltin Compounds; D014753:Vinyl Compounds; C433467:vinylphosphonic acid; C011559:tributyltin