1,3-Pentadiene reactions with carbonyl compounds

Pentadiene-l,5-diols. Alkynylepoxides undergo reductive ring opening to generate allenylsamarium iodides, which, on reaction with carbonyl compounds, deliver the unusual products. 

The indium-mediated reaction of cinnamyl bromide with 5-formyluracil derivatives gives the corresponding homoallylic alcohols. The presence of C-4 carbonyl is essential for high diastereoselectivity owing to complexation with indium (Scheme 8.32) [49]. Pentadienylindium, a vinylog of allylindium, reacts with carbonyl compounds selectively at the y position to give 1,4-pentadiene derivatives (Scheme 8.33) [50]. 

Ordinary Grignard reagents react with a, -unsaturated carbonyl compounds and afford both 1,2-adduct and 1,4-adduct. However, methylsulfonyhnethylmagnesium bromide or p-tolylsulfonylmethylmagnesium bromide gave only 1,2-adducts in the reaction with conjugated carbonyl compounds such as crotonaldehyde, cinnamaldehyde, trans-4-phenyl-3-buten-2-one, benzalacetophenone and l,5-diphenyl-2,4-pentadien-l-one. 

Complexes 17-19 can be written in one valence structure as a, /3-unsaturated carbonyl compounds in which the carbonyl oxygen atom is coordinated to a BF2(OR) Lewis acid. The C=C double bonds of such organic systems are activated toward certain reactions, like Diels-Alder additions, and complexes 17-19 show similar chemistry. Complexes 17 and 18 undergo Diels-Alder additions with isoprene, 2,3-dimethyl-1,3-butadiene, tram-2-methyl-l,3-pentadiene, and cyclopentadiene to give Diels-Alder products 20-23 as shown in Scheme 1 for complex 17 (32). Compounds 20-23 are prepared in crude product yields of 75-98% and are isolated as analytically pure solids in yields of 16-66%. The X-ray structure of the isoprene product 20 has been determined and the ORTEP diagram (shown in Fig. 3) reveals the regiochemistry of the Diels-Alder addition. The C-14=C-15 double bond distance is 1.327(4) A, and the... 

There has been one report of an rj1 -pentadienyl complex of a transition element, Cp2Zr(2-MeC5H6)2, prepared from Cp2ZrCl2 and 2-methyl-pentadienylpotassium (155). Cp2ZrHCl, however, give -complexes of 1,3-pentadiene and its higher homologs, when treated with pentadienyl-potassiums. The reactions of these products with alkenes, alkynes, dienes, and carbonyl compounds are synthetically important (156). 

Pentadienyl compounds similar to -C6H7Mn(CO)3 are also prepared by the reaction of pentadiene compounds of organotin compounds with manganese carbonyl compounds as shown in eq. (14.11) [25]. 

Transmetallation of 1-6 or treatment of 1-6 with Lewis acid further broadens the scope of its reaction chemistry. In the presence of CuCl, the reaction of 1-6 with diazo dicarboxylate affords pyridazine derivatives [27]. In the presence of CuCl or nickel complexes, the reaction of 1-6 with alkynes leads to benzene derivatives [28, 29]. Transmetallation of 1-6 with Bids allows further reaction with 2-oxo malonate to give 2/7-pyran derivatives [27]. Transmetallation of 1-6 with CrCls followed by reaction with isocyanates affords pyridine derivatives [30]. Transmetallation of 1-6 with AICI3 followed by reaction with aldehydes affords pentasubstimted cyclo-pentadiene derivatives [31]. Under the similar condition, 1-6 reacts with nitroso compounds to form pyrrole derivatives [32]. Addition of n-butyl lithium activates 1-6 and allows further reaction with carbon monoxide, which leads to carbonylation and affords 2-cyclopentenone upon hydrolysis [33]. 

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