[90330-49-7] · C13H26O3Si2 · 3-(Methoxymethylene)-2,4-bis(trimethylsilyloxy)-1,4-pentadiene · (MW 286.57)
(a reagent for reiterative Diels-Alder reactions1)
Solubility: very sol most organic solvents; decomposition occurs in protic solvents.
Purification: vacuum distillation.
Handling, Storage, and Precautions: stored safely for a few weeks in a refrigerator under nitrogen atmosphere; hydrolytic conditions should be avoided for reactions and handling.
3-(Methoxymethylene)-2,4-bis(trimethylsilyloxy)-1,4-pentadiene (1) is a reactive cross-conjugated triene and can be effectively utilized in sequential Diels-Alder reactions, which are called diene-transmissive Diels-Alder reactions,1 producing a variety of hydrobenzene and -naphthalene ring systems bearing many functional groups.
3-(Methoxymethylene)-2,4-bis(trimethylsilyloxy)-1,4-pentadiene (1) smoothly reacts, at rt, with alkynes activated by electron-withdrawing substituents. The 1:1 cycloadducts with unsymmetrical dienophiles are formed with high regioselectivity, and they undergo spontaneous elimination of methyl trimethylsilyl ether to give o-hydroxyacetophenone derivatives in moderate yields (eq 1).3a
On the other hand, the reactions of (1) with electron-deficient alkenes require heating under reflux in benzene to produce either 3-cyclohexen-1-ones (the 1:1 cycloadducts) or tetrahydronaphthalen-1-ones (the 1:2 cycloadducts), depending upon the molar amounts of the dienophiles used or the reaction temperatures applied (eq 2).3 When unsymmetrically substituted alkenes are employed (2 equiv), both the initial and second stages of the ring-forming processes are exclusively regioselective.4
Diels-Alder reactions of (1) with alkene dienophiles at rt form 1:1 cycloadducts selectively. A second ring-forming reaction can then be performed by using a variety of dienophiles. Especially, the cross reactions with alkynic dienophiles are useful, providing a convenient entry to highly functionalized tetrahydronaphthalen-1-ol derivatives (eq 3).5
Cross-conjugated trienes (2) bearing various substituents at the central double bond are accessible by applications of the synthetic procedures mentioned above.6
Ring formation using two different dienophiles can also be performed with synthetic equivalents of cross-conjugated trienes.7-10 The Grignard reagent of 2-chloro-1,3-butadiene (see 1,3-Butadienyl-1-magnesium Chloride) reacts with ketones to produce diene alcohols which serve as a versatile synthetic equivalent of cross-conjugated trienes.7,8 A typical sequence of reactions involves initial Diels-Alder reaction of 1-(1-methylene-2-propenyl)-1-cyclopentanol with Dimethyl Acetylenedicarboxylate (DMAD), dehydration of the resulting 1,4-hexadiene with molecular sieves 5A, and a second Diels-Alder reaction with DMAD to give dihydrobenz[e]indenetetracarboxylate after dehydrogenative aromatization with Chloranil (eq 4).8
Kyushu University, Kasuga, Japan