Magnesium compounds natural products synthesis

A simple two-step protocol for the generation of a terminal diene is to add allyl magnesium bromide to an aldehyde or a ketone and subsequent acid or base catalysed dehydration (equation 34)72. Cheng and coworkers used this sequence for the synthesis of some indole natural products (equation 35)72a. Regiospecific dienones can be prepared by 1,2-addition of vinyllithium to a,/l-unsaturated carbonyl compounds and oxidative rearrangement of the resulting dienols with pyridinium dichromate (equation 36)73. 

The nucleophilic substitution of a halogenocompound by an organometallic reagent (e.g. an organolithium or -magnesium) proceeds smoothly through the formation of cuprates. This technique has been applied to the synthesis of various natural products (Equation 14) and of biologically active compounds such as antibiotics (Equation 15) (see also [13]). 

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