Hydroamination of conjugated dienes

Conjugated dienes can serve as reactive substrates in both inter- and intramolecular hydroamination processes since the reactivity of the conjugated system is significantly higher than that of an isolated double bond. 

The hydroamination of dienes with basic primary and secondary amines can be achieved with a variety of catalysts including aUcah metals and their readily available derivatives. Reactions of acyclic 1,3-dienes catalyzed by alkah metals [159, 160, 171], metal hydrides [172], and metal amides (generated from metal alkyls) [163, 173, 174] result in regioselective formation of the stericaUy less hindered 1,4-addition product in most cases (23) [174]. Primary aliphatic amines are capable of performing double hydroamination in these conditions, typically leading to complex mixtures of mono- and bis-aUyl amines, whereas reactions with secondary amines are more practical [160]. 

Isolated double bonds are significantly less reactive than the conjugated diene moiety which is illustrated by the base-catalyzed regioselective hydroamination of myrcene to form diethylgeranylamine (24) [171]. This reaction is performed industrially on a multi ton scale as part of the Takasago menthol synthesis [175]. 

A few examples of rare earth metal-catalyzed diene hydroamination have been reported. The reaction apparently proceeds in line with base-catalyzed inter-molecular hydroaminations to give the 1,4-addition product when using the ansa-neodymocene Me2Si(C5Mc4)2NdCH(SiMe3)2 (16-Nd) (25) [20, 65]. 

DFT-calculations suggest that the exclusive 1,4-regioselectivity results from regiospecific insertion and protonolysis steps (see also Sect. 3.3) [176]. 

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Palladium-catalyzed 1,4-hydroamination of conjugated dienes is usually accompanied by large amounts of 2 1 telomerization product [21,22]. It was shown that the use of an amine hydrochloride as a cocatalyst increased the selectivity for the 1,4-hydroamination product [23]. Thus, 1,3-butadiene and 2-3-dimethylbuta-1,3-diene gave a fair yield in the palladium-catalyzed 1,4-amination shown in [Eq.(5)]. 

The use of carbamates as the nucleophile allowed extension of the method to the gold-cataWzed intermolecular hydroamination of conjugated dienes at room temperature. The reaction took place regioselectively as 1,2-addition at the less substituted double bond. 

Representative procedure for the gold-catalyzed hydroamination of conjugated dienes. Benzyl 3-methylpent-3-en-2-ylcarbamat ... 

Nickel-catalyzed hydroamination of conjugated dienes at room temperature has been shown to be an efficient synthesis of allylamines in excellent yields [262],... 

Organolanthanide-catalyzed hydroamination of conjugated dienes is a facile process due to the transient formation of an 7 -allyl intermediate, which forms E/Z-vinylpyrrolidines and vinylpiperidines upon protonation, and, under certain conditions, also aUyl isomers (Fig. 11, Scheme 12). Cychzations with lanthanocenes... 

The intermolecular addition of carbamates to 1,3-dienes (equation 147) under mild conditions has been described as well. The hydrothiolation of 1,3-dienes has also been reported. " Other related conjugate additions can be performed over methylenecyclopropanes (equation 148) with sulfonamides and the resulting product cyclizes by a second hydroamination of an olefin, finally yielding cyclic sulfonamides. This behavior is reproduced in a similar reaction for the ring opening of vinylcyclopropanes with sulfonamides. One more example in this group of reactions is the synthesis of dUiydrobenzofurans from aryl-allyl ethers. ... 

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