Solvent-Free C-X Bond Formation

Type of reaction C-halogen bond formation Reaction condition solid-state 

Keywords cinnamic acid, stilbene, halogenation, addition, gas-solid reaction 

00 g (5.6 mmol) of powdered mmv-stilbene 1 was treated with Cl2 gas (500 mL, 22 mmol) at room temperature for 6 h. After removing excess Cl2 gas, the reaction mixture was chromatographed on silica gel (benzene-n-hexane, 1 10) to give a 61 39 mixture of dl- and meso-2b (0.55 g, 39%) along with recovered 1 (0.60 g, 60%). The yield of 2b was increased to 100% and the cis-ad-dition strongly enhanced, if the crystals of 1 were ball-milled to pm size prior to a very slow addition of the Cl2 at 0 °C (0.05 bar, 3 h) and then 0.5 bar Cl2 (24 h). 

Similar results were obtained if powdered or ball-milled /nms-stilbene 1 was treated with the stoichiometric amount of Br2 gas to give meso- and dl-2a. 

Solvent-free organic Synthesis. Kiochi Tanaka 

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