Dimethylacetylenedicarboxylate DMAD

Fig. 4.12. Reaction of thiophene III with dimethylacetylenedicarboxylate (DMAD) E = C02Me.

Cycloaddition reactions, [3 + 2] or [2 + 2] depending on L, of TpRe(CO)(L) (f/ -furan) complexes have been reported. The electrophilic alkene tetracyano-ethylene (TCNE) and the alkyne dimethylacetylenedicarboxylate (DMAD) were used as dienophiles. For L = PMcs and BuNC, 1,3-dipolar cycloaddition of TCNE to / -furan gives [3 + 2] products via a carbonyl ylide (Scheme 47). Addition of... 

However, 1,3-dipolar cycloaddition of acetylenic dipolarophiles such as dimethylacetylenedicarboxylate (DMAD) have been reported. Thus, thiazole and its alkyl derivatives undergo condensation with dimethyl acetylenedicarboxylate, giving 1 2 adducts. For example, Potts et al. reported that thiazole when quartemized as an ylide with alkylators such as bromoacetophenone (BrCH2COPh), undergoes 1,3-dipolar cycloaddition... 

Reaction of 41 with terminal alkynes leads to vinyl complexes 43, with excess alkyne leading to bridging vinylidene 44, in respectable yield.Reactions similar to the transformation 41 43 occur with electron-deficient non-terminal alkynes such as dimethylacetylenedicarboxylate (DMAD) or hexafluorobut-2-yne. 

The action of dimethylacetylenedicarboxylate (DMAD) on lithium salt of 2,3,4,5,7,8-hexafluoro -quinolinthiole 124 leads to 74 % of 4,6,7,8,9-pentafluoro-thieno[3,2-c]quinoline 125 and 13 % dimethyl l-(2,3,5,6,7,8-hexafluoro-4-quinolyl-thio)ethen-l,2-dicarboxylate (Schane 61) [91]. 

Although ruthenacyclopentadiene intermediates are able to coordinate a third molecule of alkyne to afford benzene derivatives, catal3Aic intermolecular [2+2+2] cycloadditions involving three nontethered a]k3mes are seldom because of their low selectivity. For example, substituted o-phtalates could be chemoselectively obtained by reaction of two equivalents of terminal alkynes with dimethylacetylenedicarboxylate (DMAD) [11] or by cycloaddition of an internal alkyne, a terminal alkyne and DMAD [12] [Eq. (8)] in the presence of the Cp RuCl(cod) complex. 

In contrast, product mixtures were obtained [53] when a-substituted styrenes were reacted with dimethylacetylenedicarboxylate (Equation 2.19). The products were formed via aromatization of the primary cycloadducts or by cene addition of a second molecule of DMAD. 

MP = methylpropiolate BQ = 1,4-benzoquinone MA = maleic anhydride DMAD = dimethylacetylenedicarboxylate TCNE = tetracyanoethylene... 

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