The Synthesis and Chemistry of 8‐Substituted Bicyclo[5.1.0]oct‐1(8)‐ene

Abstract

8‐Bromobicyclo[5.1.0]oct‐1(8)‐cne (7), an intermediate for the preparation of 8‐substituted bicyclo[5.1.0]oct‐1(8)‐enes, was synthesized by denomination of 1,8,8‐tribromobicyclo[5.1.0]octane (6). Compound 7 underwent bromo‐lithium exchange followed by nucleophilic substitution reactions to generate bicyclo[5.1.0]oct‐1(8)‐ene (5), 8‐methylbicyclo[5.1.0]oct‐1(8)‐ene (10), and 8‐trimethylsilylbicyclo[5.1.0]oct‐1(8)‐ene (11). The bicyclic cyclopropenes 7, 5, 10, and 11 reacted with cyclopentadiene to form adducts 12, 13, 14, and 15, respectively. All of these Diels‐Alder adducts are endo‐exo isomers (endo‐addition from the view of the cyclopropene and exo‐addition from the view of the cyclooctene).

Regio‐ and Stereoselectivity of Ene Reactions: The Dimerization of Bicyclic 1,3‐Fused 2‐(Trimethylsilyl)cycloprop‐1‐enes

“…[13] Compound 10 was generated from cycloheptene. The cycloalkene reacted by bromination, dehydrobromination and dibromocarbene addition to give tribromocyclopropane 10 (Scheme 1).…”

“…of methyllithium in diethyl ether at -78°C generated cyclopropenyl anion 12, which was treated with trimethylsilyl chloride to produce 4. [13] Cyclopropene 4 was trapped with cyclopentadiene to give the corresponding [4+2] cycloadduct 14.…”

“…After compound 4 had been synthesized and purified at low temperature, it was kept neat at room temperature for 1 day and a sole stable product 6 (Scheme 1) was isolated in 92 % yield. According to spectral analysis (MS: m/z = 360; 13 C NMR: δ = 145.4 and 114.4 ppm; IR: ν = 1772 cm -1 ), compound 6, with a dimeric mass and a cyclopropenyl group, is an ene dimer of 4.…”

“…The higher analogue, compound 5, was also synthesized and isolated at room temperature and was then stirred at 50°C for two weeks: product 7 was isolated as the sole stable product in 90 % yield. According to its spectra (MS: m/z = 388; 13 C NMR: δ = 145.9 and 118.1 ppm; IR: ν = 1758 cm -1 ), compound 7, with a dimeric mass and cyclopropenyl group, is an ene dimer of 5. The structure of 7 was determined by single-crystal X-ray analysis ( Figure 5).…”

“…All spectroscopic data for compound 10 are in agreement with literature values. [13] 1,9,9-Tribromobicyclo[6.1.0]nonane (11): A modification of a previously reported procedure was used. [16] A mixture of 1-bromocyclononene (18.9 g, 100 mmol) and bromoform (26 mL), 50 % sodium hydroxide (26 mL) and tetra-n-butylammonium bromide (0.1 g) were placed in a 100 mL flask.…”