Coupling couplings with ethyl crotonate

Isayama described the coupling reaction of N-methylimine 157 and ethyl crotonate catalyzed by Co(acac)2 and mediated by PhSiH3 to produce Mannich product 158 in 82% with syn-selectivity (Scheme 41) [71]. The (i-laclam 159 was readily synthesized by heating 158. In 2002, Matsuda et al. reported cationic Rh complex [Rh(COD) P(OPh)3 2]OTf (1 mol%) as an active catalyst for the reductive Mannich reaction [72]. N-Tosylaldiminc 160 was coupled with methyl acrylate and Et2MeSiH (200 mol%) at 45 °C to give the b-amino ester 161 in 96% with moderate anti-selectivity 68%. 

Simple alkyl acrylates have been used as partner in mixed hydrocoupling reactions in a number of cases (Table 14). Like mixed couplings with 7, LHD formation and hydrogenation compete with formation of the MHC of alkyl acrylates. Coelectrolysis of ethyl 3,4-dimethoxycinnamate Ey z= —1.94 V) with ethyl crotonate Ey = —2.37 V) in a molar ratio of 1 7.2 in MeCN at E = —2.03 V gave none of the MHC bW only the CHD of the cinnamate. The only product derived from the crotonate was diethyl 2-ethylidene-3-methylglutarate (49%) formed by action of an EGB, most likely the dimer dianion of the cinnamate [61]. 

Contrary to the results with ethyl acrylate, which affords 5-carbofunctional pyrimidines, palladium-catalyzed C-C coupling with ethyl methacrylate or ethyl crotonate directly gives the corresponding pyrido[2,3-r/]pyrimidin-2(l//)-ones l.139... 

The reductive coupling of ketones or aldehydes with electrophilic alkenes such as conjugated esters (Scheme 52) has been described independently by Inanaga et al. [38] and Fukuzawa et al. [123,124]. The reaction was performed in THF either in the presence of HMPA [38] or an alcohol [123,124]. The mechanistic aspects of this reaction have been discussed [ 124]. Presumably, the ketyl radical or its protonated form adds to ethyl acrylate with formation of the C-C bond. An efficient enantioselective synthesis of v-butyrolactones has been derived by using AT-methylephedrinyl acrylate or crotonate [125]. One example (synthesis of 33) is indicated in Scheme 52. 

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