Trisubstituted ethenes

What is of immediate interest are the various XRD determinations of B—C bond lengths in classical methyleneboranes, exemplified by 55 and 56, which are 1.391 and 1.631 A, respectively.60 Furthermore, the C=B—C linkage is essentially linear (179.6(3) A). The observed B—C bond length is only somewhat longer than the C=C bond in a trisubstituted ethene (1.35 A). Thus there is no doubt that some boraethenes have a genuine B=C bond. 

The increments AJ in Table 1 can be used to predict geminal 1H,13C coupling constants in di-and trisubstituted ethenes, and a remarkable agreement with experimental values can be achieved, for example ... 

The work by Armstrong was extended to include the room temperature resin capture of trisubstituted ethenes with a pendant boronate group.80 Modification of the amide linker above to a novel silyl-based one allowed for the traceless cleavage of superior analogues. 

Bis(ethene)(toluene)iron catalyses the cyclotrimerization of alkynes to derivatives of benzene terminal alkynes RC=CH (R = t -Bu, Ph or C02Me) yield mainly 1,2,4-trisubstituted benzenes 560, while dimethyl acetylenedicarboxylate furnishes the iron complex 561. ... 

Acyclic Disubstituted and Trisubstituted Ethenes 6.9 Trisubstituted ethenes... 

Alkynes as well as alkenes are also recognized as readily available building blocks for constructing alkenylarenes. The reactions of (hetero)arenes with alkynes can be performed without any oxidant through C-H bond cleavage and alkyne insertion steps. Early examples of such hydroarylation of alkynes were reported by Hong and coworkers [74]. Benzene and furans react with diphenylacetylene in the presence of Rh4(CO)i2 catalyst at 220°C under CO (25kgcm ) to produce trisubstituted ethenes (Scheme 18.74). 

Diketones can be obtained by the Michael-type reaction of trialkyl-alkynylborates with methyl vinyl ketone in the presence of TiCl4 (Scheme 5). The reactions of bis(trimethylstannyl)butadiyne with trialkylboranes also involve alkynylborates. Use of 9-BBN derivatives has advantages for the synthesis of trisubstituted ethenes from lithium alkenyltrialkylborates. Alkenylborates for such reactions can be obtained from the corresponding tosylhydrazones. ... 

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