Allenes and Dienes

Krause has reported a gold(I)-catalyzed protocol for the intramolecular mdo-hydro-thiolation of a-thioallenes to form 2,5-dihydrothiophenes [67]. As an example, 

Puddephatt, R.J. (1982) Comprehensive Organometallic Chemistry, vol. 2 (eds G. Wilkinson, F.G.A. Stone, and E.W. Abel), Pergamon Press, Oxford, pp. 762-821. 

---

Some cases are known in which Diels-Alder reactions of electron-deficient allenes and dienes compete with [2 + 2]-cycloadditions (see also Section 7.3.7) [12, 151, 335, 336]. Recently, a phosphane-catalyzed [4 + 2]-annulation starting from allenic ester 337 and N-tosylaldimines 338 was published [337]. However, the formation of the tetrahydropyridines 339 isolated in excellent yields is explained by a multi-step mechanism and only resembles a Diels-Alder reaction. 

Thermal sigmatropic 1,5 hydrogen shifts are quite common in certain allene and diene systems, cis- 1,3-Dienes have the proper geometric arrangement to undergo a thermally allowed suprafacial hydrogen shift, cis-1,3-Hexadiene, for instance, gives... 

While intermolecular hydroamination of simple alkenes remains a great challenge as of now, addition of amines to alkynes, allenes, and dienes proceeds more easily. However, the addition of an amine to a polyene moiety may not necessary result in the formation of a new stereocenter, if an imine is generated (Scheme 11.18). 

Scheme 11.18 Intermolecular hydroamination of alkynes, allenes, and dienes.

The metal-catalyzed reaction between allenes and dienes was also investigated and was found to be highly efficient in many cases. For... 

Generation of Phosphorus Ylides and Phosphonate Anions. NaHMDS isthemostutiUzedbaseforthedeprotonation of a variety of phosphonium salts to generate the corresponding ylides, which then undergo Wittig reaction with a carbonyl compound. More recently, it was shown that such a base is compatible with a variety of other systems. For instance, it was shown that allenes and dienes could be prepared, respectively, from aromatic and alicyclic aldehydes when reacted with (Me2N)3P=CH2 in the presence of 4 equiv of NaHMDS and titanium trichloride iso-propoxide (eqs 30 and 31). ... 

RXN8 Tandem HECK-Anion Capture Process of Alkenes, Alkynes, Allenes and Dienes... 

The reactions of allenes and dienes with iron and ruthenium compounds form a large number of various allyl complexes (see allene complexes). Osmium forms allyl compounds of the formulas [OsCl(C3H5)(PPh3)3] and [Os(C8Hg)(CO)3]. 

Pd-Catalyzed Carboamination Reactions of Alkynes, Allenes, and Dienes... 

Scheme 19 Regioselective hydroaminomethylation of allenes and dienes via 2-piopanol-mediated reductive coupling with formaldimines. Yields are of material isolated by flash chromatography on silica gel. dCypm = biY-(dicyclohexylphosphino)methane, dCype = 6 -(dicyclohexylphosphino)ethane...

Some other cycloaddition reactions obtained from allenes and dienes are listed in Table 6.10. 

As this chapter deals with only carboamination reactions for stereoselective C-N bond formation, discussions of alkyne, allene, and diene carboamination reactions are beyond the scope. 

Allenes and dienes also react with phosphinic acid or its anilinium salt, typically in the presence of Pd2(dba)3/xantphos (1 mol%) at 110°C (Scheme 57) [61]. Acetonitrile and DMF are the solvents of choice for phosphinic acid and DMF for the anilinium salt. 3,3-Disubstituted allenes and phenylallene react with phosphinic acid regioselectively and with a high -selectivity to furnish ally lie //-phosphinic acids in moderate to high yields. On the other hand, the regio- and stereoselectivities observed for 3-alkylallenes are low, but can be significantly improved using the anilinium salt. 

---