Mechanistic Considerations of the Enone-Olefin Photocycloaddition 1,4 Adducts Exciplex Adducts Possibility of alkene Product Alken Enone A note on light sources The source of light is usually a met used to remove light below a certain wavelength. The two most ommon are Pyrex glass, which allows light with2>29 can als wavelength to num"glass, which allows light with i>350 nm vIa s Schuster, D L, et a. Chem. Rev. 1993, 93. 3. (±)β- BulInesene and Epi-B- bulnesene Unknown I 1)MeMgl, Et. rt. 3 h OAC OAC c:B33:1 and 23% 67% :1-Epi阝- bulnesene Stereochemical rationale (TBD) B: B-Bulnesene Oppolzer, W, et al. He/v Chim Acta, 1980, 63, 1198 36A-02 handout3/31/001:30PMMechanistic Considerations of the Enone-Olefin Photocycloaddition Schuster, D.I., et al. Chem. Rev. 1993, 93, 3. Enone Enone1 Enone3 Alkene 1,4 Biradical3 Adducts 1,4 Biradical1 Adducts Product O hν Inter￾System Crossing Exciplex Inter￾System Crossing Product formation Reversion to starting materials O 1 O 3 O X X O X O X 3 3 O X O X 1 1 + + O X Enone O Alkene X + 3 Decay ? ? Possibility of alkene isomerization The source of light is usually a mercury lamp. A filter is usually used to remove light below a certain wavelength. The two most common are Pyrex glass, which allows light with λ > 290 nm to pass, and "uranium" glass, which allows light with λ > 350 nm wavelength to pass. A note on light sources: O X This product can also arise via similar intermediates (±) β-Bulnesene and Epi-β-bulnesene O OAc Me H O Me hν, Pyrex, c-Hex, rt, 3 h α:β 3.3: 1 Oppolzer, W., et al. Helv. Chim. Acta., 1980, 63, 1198. OAc H Me H O OAc H Me H O H Me OAc Me MsO OH 1) MeMgI, Et2O Me O H Me H Me Me HO OH Me H Me Me Me 2) KOH, dioxane 67% MsCl, NEt3 Ph3P=CMe2 72% α: 1-Epi-β-bulnesene β: β-Bulnesene Major Product Stereochemical rationale (TBD) Grob 76% Unknown mixture 67% Prepared in 5 steps and 23% yield from 3-methyl-5-bromo-1-pentene 36A-02-Handout 3/31/00 1:30 PM