Grignard reagents with dienes

The reaction of Grignard reagents with pyran-2-ones at low temperature leads to 2,2-disubstituted 2//-pyrans (61CB1784). These appear to exist solely in the pyran form since they do not form 2,4-dinitrophenylhydrazones and their UV spectra are similar to those of y-cfs-dienes. 

Terminal enynes Reaction of aryl Grignard reagents with pyridazine 1-oxide leads exclusively to terminal (E)-enynes in 50-75% yield. Alkyl Grignard reagents lead to 1,3-dienes in rather low yield. 

Coupling of Grignard reagents with allylic acetates (5, 226). This reaction has been extended to a l-acetoxy-2,4-diene for a synthesis of the sex pheromone of the codling moth (3)." ... 

Reaction of pyridazine 1-oxide with phenylmagnesium bromide gives 1,4-diphenyl-butadiene as the main product and l-phenylbut-l-en-3-yne and 3,6-diphenylpyridazine as by-products, while alkyl Grignard reagents lead to the corresponding 1,3-dienes exclusively (79JCS(P1)2136>. 

This procedure illustrates a general method for the preparation of 2-hydroxybicyclo[3.2.0]heptanes by copper(I)-catalyzed photobicyclization of 3-hydroxy-1,6-heptadienes, and a general route to the requisite dienes from allyl alcohols by conversion to 4-pentenals and treatment of the latter with vinyl Grignard reagents. 

Allyltin compounds can be prepared by simple modifications of the usual reaction involving allyl Grignard reagents (139), by the 1,4-addition of trialkyltin hydrides to 1,3-dienes 140,141), or by the reaction of an aldehyde or ketone with the appropriate, tin-carrying, Wittig reagents (142). 

The parent compound, 69, has been synthesized and characterised <2003ZFA1475>. 4-Chloro-hepta-l,6-diene was reacted with Mg. No Grignard rearrangement was noticed but instead the Grignard reagent was converted into l-allyl-3-butenylphosphonous dichloride by reaction with PC13. Reduction with LiAlH. produced l-allyl-3-butenyl-phosphane. Radical-initiated cyclization led to the product, l-phosphabicyclo[3.3.0]octane. Four derivatives were similarly prepared and characterized (70-73). Compound 74 was similarly prepared via a radical reaction < 1997PS(123)141 >. 

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