A Novel Method for the Construction of (Z,E)- or (Z,Z)-Conjugated Alkadienyl Carboxylates

Abstract

[reaction: see text] The stereocontrolled dehydrobromination of 1,2-dibromoethyl carboxylates giving (Z)-2-bromovinyl carboxylates could readily be approached by using DBU and a catalytic amount of hydroquinone as a base at -78 degrees C. The first investigation on the Suzuki-type cross-coupling of (Z)-2-bromovinyl carboxylates as electrophiles with stereodefined alkenylboronic acids provides a novel method for the construction of (Z,E)- or (Z,Z)-conjugated alkadienyl carboxylate moieties, which are often present in a range of natural products.

Metal-Catalyzed Synthesis and Transformations of β-Haloenol Esters

“…Remarkably, the asymmetric hydrogenation of compounds 31 to afford the corresponding chiral homobenzylic esters 32, of interest as precursors of synthetically useful chiral alcohols by deacylation, could be successfully accomplished by the same authors employing rhodium(I) catalysts containing optically pure bidentate phosphine-phosphite ligands (ee up to 98%) [59,61]. As shown in Scheme 18, the Suzuki-Miyaura coupling of (Z)-2-bromovinyl esters 34, generated by stereocontrolled dehydrobromination of 1,2-dibromoethyl esters 33 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and a catalytic amount of hydroquinone, with stereodefined alkenylboronic acids provided also an efficient route for the selective construction of (Z,E)-and (Z,Z)-conjugated dienyl esters (35 and 36, respectively), molecules of enormous interest since they can be employed as precursors for the preparation of several natural products through Diels-Alder reactions [75]. As shown in Scheme 18, the Suzuki-Miyaura coupling of (Z)-2-bromovinyl esters 34, generated by stereocontrolled dehydrobromination of 1,2-dibromoethyl esters 33 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and a catalytic amount of hydroquinone, with stereodefined alkenylboronic acids provided also an efficient route for the selective construction of (Z,E)-and (Z,Z)-conjugated dienyl esters (35 and 36, respectively), molecules of enormous interest since they can be employed as precursors for the preparation of several natural products through Diels-Alder reactions [75].…”

“…As shown in Scheme 18, the Suzuki-Miyaura coupling of (Z)-2-bromovinyl esters 34, generated by stereocontrolled dehydrobromination of 1,2-dibromoethyl esters 33 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and a catalytic amount of hydroquinone, with stereodefined alkenylboronic acids provided also an efficient route for the selective construction of (Z,E)-and (Z,Z)-conjugated dienyl esters (35 and 36, respectively), molecules of enormous interest since they can be employed as precursors for the preparation of several natural products through Diels-Alder reactions [75]. As shown in Scheme 18, the Suzuki-Miyaura coupling of (Z)-2-bromovinyl esters 34, generated by stereocontrolled dehydrobromination of 1,2-dibromoethyl esters 33 with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and a catalytic amount of hydroquinone, with stereodefined alkenylboronic acids provided also an efficient route for the selective construction of (Z,E)-and (Z,Z)-conjugated dienyl esters (35 and 36, respectively), molecules of enormous interest since they can be employed as precursors for the preparation of several natural products through Diels-Alder reactions [75]. In addition, the tetrasubstituted olefins 37-40 (see Figure 5) were also synthesized in high yields (72%-99%) by Suzuki-Miyaura coupling of the corresponding β-haloenol acetates with boronic acids (the C-C bond formed is highlighted in bold) [28,31,71].…”

Strategies towards the Synthesis of the Gilvocarcins

“…As 11 is a commercially available reagent, the synthetic problem was reduced to the preparation of its diene partner 12. Conceptually, it could be formed by Sonogashira coupling between alkyne bearing glycoside 18 and known 1-acetoxy-2-bromoethylene (19) 14 and a further partial re-duction of the triple bond (Scheme 6). Known alkyne 18 was prepared as a single stereoisomer from D-fucose following our previous work.…”

Palladium‐Catalyzed CC Bond Formation

“…Organometallic reagents of low nucleophilicity, for example nitroaryl stannanes [69], undergo transmetalation only slowly; this can lead to low yields of crosscoupling products [69]. Palladium-catalyzed cross-coupling reactions of boron derivatives [18,[66][67][68]. 283 Scheme 8.4.…”