The Synthesis of Allenes from 1,1-Dihalocyclopropane Derivatives and Alkyllithium.

The Use of Flow Chemistry for Two-Phase Dibromocyclopropanation of Alkenes

“…Yield was 0.26 g of a mixture containing the dibromide 7-tetrabromide 8-bromoform in Table 2. Dihalocyclopropanation of a selection of alkenes using 40% (w/w) NaOH (aq) at AO ratio: 4 1 H NMR. Estimated yield of 7 was 0.22 g, 65%, and of tetrabromide 8, 0.038 g, 9%.…”

“…The solvents were carefully removed in vacuo at/or just below room temperature. Yield was 0.34 g of a mixture containing the dibromide 9-bromoform, 63:37, according to 1 H NMR. Estimated yield of 9 was 0.21 g, 57%.…”

“…In the work-up procedure, ethyl acetate replaced pentane, and the product mixture was purified by filtration through a plug made of 1 cm aluminum oxide, using pentane as the eluent. Yield was 0.32 g of a mixture containing the dibromide 6-bromoform, 94:6, according to 1 H NMR. Estimated yield of 6 was 0.30 g, 81%.…”

“…The routine NMR spectra were recorded using CDCl 3 as a solvent and TMS as a reference. 1 H NMR spectra were recorded at 300 or 400 MHz, and 13 C NMR spectra were recorded at 75 or 100 MHz. NMR resonances are given only when literature spectra are not found or when our spectra have significantly better resolution than previously reported spectra.…”

“…gem-Dibromocyclopropanes are important substrates in organic synthesis where they have been used as versatile intermediates for the syntheses of other interesting compounds like allenes [1,2], cumulenes [3], cyclopentadienes [4,5], cyclic acetals [6,7], and furans [8]. They have also been found useful in the syntheses of many natural products, as emphasized in several reviews [9][10][11].…”