Kinetics and Regioselectivity of Ring Opening of 1-Bicyclo[3.1.0]hexanylmethyl Radical

Abstract

Rate constants for the rearrangement of 1-bicyclo[3.1.0]hexanylmethyl radical (2) to 3-methylenecyclohexenyl radical (3) and 2-methylenecyclopentyl-1-methyl radical (1) were measured using the PTOC-thiol competition method. The ring-expansion pathway is described by the rate equation, log(k/s-1) = (12.5 +/- 0.1) - (4.9 +/- 0.1)/theta; the non-expansion pathway is described by log(k/s-1) = (11.9 +/- 0.6) - (6.9 +/- 0.8)/theta. Employing the slower trapping agent, tri-n-butylstannane, favors methylenecyclohexane over 2-methyl-methylenecyclopentane by more than 120:1 at ambient or lower temperatures.

Isothiourea-Mediated Asymmetric Functionalization of 3-Alkenoic Acids

“…The combined organic extracts were dried (MgSO 4 ), filtered, and concentrated in vacuo to give ethyl 2-(cyclopent-1-en-1-yl)acetate 64 as a light yellow oil (5.68 g, 97%): δ H (500 MHz, CDCl 3 ) 1.29 (3H, t, J 7.1, C H 3 ), 1.93 (2H, quintet, J 7.5, C H 2 ), 2.33–2.38 (4H, m, C H 2 and C H 2 ), 3.14 (2H, s, C H 2 CO 2 Et), 4.17 (2H, q, J 7.1, C H 2 CH 3 ), 5.55–5.57 (1H, m, C H ). Data are in accordance with the literature …”

“…39 Ethyl 2-(cyclopent-1-en-1-yl)acetate 64. Following a literature procedure, 40 to a solution of DIPA (5.82 mL, 41.2 mmol) in THF (80 mL) at 0 °C was added 2.5 M n-BuLi (16.5 mL, 41.2 mmol), and the reaction mixture was stirred at that temperature for 30 min. The reaction mixture was cooled to −78 °C, and a solution of ethyl 2-(cyclopent-1-en-1-yl)acetate 63 (5.88 g, 38.2 mmol) in THF (25 mL) was added dropwise over 15 min before stirring for a further 20 min.…”

“…Data are in accordance with the literature. 40 2-(Cyclopent-1-en-1-yl)acetic acid 15. Following a literature procedure, 41 a solution of ethyl 2-(cyclopent-1-en-1-yl)acetate 64 (4.15 g, 27.0 mmol) in 0.5 M KOH (80.8 mL, 40.4 mmol) was heated at reflux for 16 h. Once cooled to rt the reaction mixture was extracted with Et 2 O (×3).…”