Ring-closure variants utilizing highly reactive -carbonyl-ylides

Ring-closure variants utilizing highly reactive to-carbonyl-ylides 

1 Simple example of a ring-closure reaction of oo-halo-ylides and synthesis of small rings featuring exocyclic alkenes 

Synthesis of (4-bromo-butyl)triphenylphosphonium bromide 1. Charge a single-necked round-bottomed flask (250 mL) with triphenylphosphane (13 g, 50 mmol), 1,4-dibrombutane (12 g, 57 mmol), toluene (50 mL), and a magnetic stirrer bar. Equip the flask with a condenser and put it in an oil bath mounted on a hot-plate stirrer. 

Heat and stir the mixture at 100°C for 14 h, whereupon a precipitate of the product phosphonium salt will form. Let the flask cool to ambient temperature, filter the suspension over a Buchner funnel, and wash the crude solid repeatedly with 100 ml portions of hot toluene to remove residual tri-phenylphosphane. Dry the product in vacuo at 100°C to obtain a crystalline colourless solid, m.p. 207°C, 23 g (97%). It is sufficiently pure for the next step, but may be recrystallized from chloroform/acetone. 

Assemble a set-up consisting of a single-necked flask (250 mL) with a stop-cocked side-arm and charged with the above phosphonium salt (9.56 g, 20 mmol), and a water-cooled reflux condenser topped by a mercury float valve. Connect the set-up to a source of dry nitrogen and flush it thoroughly. 

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