Procedure:  50 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Prepared a suspension of 1.427 g of freshly pulverized Mg shavings and 0.050 g of I₂ in 5.0 mL of dry THF.  Stirred;  cooled to 0 C.  Added a solution of 1.80 mL of alkylbromide I in 2.5 mL of THF dropwise over 10 min. with slight warming.  After addition of I the mixture was stirred for 15 min and a solution of 1.348 g of aldehyde V in 5.0 mL of THF was added dropwise over 10 min.  After addition of V the reaction mixture was stirred for 15 min.  TLC (10:90 EtOAc-hexanes, PMA) showed product spot at Rf 0.38.  The reaction was quenched with sat. aq. NH₄Cl and extracted with Et₂O.  The organic layer was dried over MgSO₄, filtered and the solvent was removed by rotary evaporation.  The residue was purified by Kugelrohr distillation (85 C, 0.6 mm).  The product was a clear, colorless oil. 

 

¹H NMR (CDCl₃, 500 MHz) d 5.66 (dt, J = 15.3, 6.3 Hz, H3), 5.43 (dd, J = 15.4, 7.2 Hz, H4), 4.01 (m, H5), 2.03 (dq(apparent pent.), J = 6.8 Hz, H2), 1.54-1.20 (m, CH₂s), 0.97 (t, J = 7.5 Hz, H1), 0.86 (t, J = 6.9 Hz, H13). 

 

notes

 

It has been demonstrated that the formation of Grignard reagents most likely involves a radical process.

 

The mechanism for the addition of Grignard reagents probably involves a six-membered transition state consisting of a ternary complex...