2.3- dimethyl-2-butene-l, 4-diyl

Scheme 1 Reaction of (2,3-dimethyl-2-butene-l,4-diyl)magnesium with a soft electrophile, followed...

When this approach is applied to the magnesium complexes of acyclic 1,3-dienes, it provides an easy route to both spiro y-lactones and y-lactones. Scheme 5 gives an outline for the synthesis of spiro y-lactones from (2,3-dimethyl-2-butene-l,4-diyl)magnesium 18. 

As shown in Scheme 8, reaction of (2,3-dimethyl-2-butene-l,4-diyl)magnesium 18 with an imine afforded the 1,2-addition adduct 27, which after treatment with carbon dioxide, acidic hydrolysis, and subsequent heating afforded a y-lactam 30 accommodating a quaternary carbon center in 62% isolated yield. For other examples of this type of transformation, see Table 7. 

Scheme 4.7 illustrates a route for the synthesis of a y-lactam from the (2,3-dimethyl-2-butene-l,4-diyl)magnesium intermediate (2). Initially, treatment of 2 with A -benzylidenebenzylamine at -78°C resulted in the formation of the... 

Guaiacic acid [4,4 -(2,3-dimethyl-l-butene-(l,4-diyl)-bis-(2-methoxyphenol)] [500-40-3J M... 

In contrast, Rieke magnesium reacts with ( , )-1,4-diphenyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, isoprene, myrcene, or 2-phenyl-1,3-butadiene in tetrahydrofuran (THF) at ambient temperature to afford the corresponding substituted (2-butene-1,4-diyl)magnesium complexes in near quantitative yields. The structures of these complexes have not yet been determined except for (l,4-diphenyl-2-butene-l,4-diyl)magnesium, which has been shown to be a five-membered ring metallocycle [5]. Accordingly, the most likely structures for these complexes are five-membered metallocycles or oligomers. It is also possible that an equilibrium exists between these various forms. 

For example, dichlorodimethylsilane reacted with (l,4-diphenyl-2-butene-I,4-diyl) magnesium at — 78 C to give c/s-1,1-dimethyl-2,5-diphenylsilacyclopent-3-ene in 66% isolated yield (Table 5, entry 1). Asymmetrically substituted silicon-containing heterocycles can also be prepared in this fashion (see Table 5, entries 3-5). 

The 4,7-dimethyl-substituted 4,7-dihydro-l, 3-dithiepin (220) could be obtained by LAH reduction of ne50-hex-3-en-2,5-diyl dithiocyanate (219) and treatment with paraformaldehyde (Equation (40)) <93CC246>, and 2-alkylidene-4,7-dihydro-1,3-dithiepins, for example (222), which are useful as pharmaceutical intermediates, have been synthesized by reaction of C—H acidic substrates with sodium hydride, followed by condensation with CS2 and cyclization of intermediate (221) with (Z)-l,4-dichloro-2-butene (Scheme 37) <85GEP228255, 86JPR215>. 

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