Homopropargylic amines from

Scheme 26 Synthesis of 2-aikyl-4-halo-1 -tosyl-1,2,5,6-tetrahydropyridines from A-tosyl homopropargyl amine and aldehydes using FeX3 as promotor...

Cyclization to six-membered rings (Eq. 15) provided modest diastereoselectivity and required the use of bulkier PhMeSiH2 to prevent olefin hy-drosilylation. Propargyl and homopropargyl amines 94 afforded a variety of heterocycles (Scheme 21), if the catalyst was added slowly over the reaction course to diminish side reactions resulting from metal coordination to the basic amine [56]. The reaction procedure was extended to the diastereoselect-ive bicyclization of dienyne substrate 95, giving 96 as product in a cascade fashion (Eq. 16) [57]. 

The additional a-substitution in allenylborane reagents such as 25,28, and 30 compared to 17 enhances the enantioselectivity for the propargylation of aldehydes. However, this effect is particularly apparent in their additions to /V-H aldimines, which produce homopropargylic amines in good yields (91%), but disappointing ee (from PhHC=NH, 73% ee). With 32 (325 935677-62-6 32/ 929082-37-1), the homopropargylic amine 33 is produced as essentially a single isomer (51-85%, >99 syn, 92-99% ee) (eq 13). ... 

Allenyltrichlorosilanes can also be prepared by Sn2 displacement of propargylic chlorides with a Cu or Ni complex of HSiCl3 [56]. The reaction requires an amine base and a donor solvent such as THF or propionitrile (Table 9.32). Conditions can be adjusted to favor the propargylic or allenic silane, which is not isolated, but treated directly with various aldehydes to afford allenylcarbinols (A) or homopropargylic alcohols (B). These reactions presumably proceed by an SE2 pathway, such that the allenyl products arise from the propargylic silane and vice versa. 

In a subsequent study, Miginiac and coworkers examined additions of allenylzinc reagents to an ZV-TMS imine derived from the mono diethyl acetal of acetylene dicarboxaldehyde10. These additions afforded the homopropargylic adducts as the free primary amines (equation 13). 

As a general rule, allylic organozinc reagents do not react with unactivated a, ji-disubstituted alkynes. A few exceptions to this trend have been observed in the case of substrates bearing an appropriately located heteroatom such as the homopropargylic tertiary amine 147. The latter reacted regioselectively with allylzinc bromide but led to a 67/33 mixture of two geometric isomers, apparently derived from syn and anti additions (equation 71)82,105. 

Intramolecular additions of alcohols or amines to olefins are recognized as useful methods to provide heterocyclic compounds. Kozmin and Zhang have achieved a gold-catalyzed synthesis of heterobicyclic alkenes by double cyclization of alcohols or sulfonamides which have a 1,5-enyne moiety [175]. As a typical example, unsaturated alcohol (95) is smoothly converted to 6-oxabicyclo[3.2.1]octane (96) in 90% yield using a 5 mol% of AuCls catalyst (Scheme 18.34). Cyclic ethers are also available from homopropargylic ethers with pendant alcohols through gold-catalyzed... 

On the other hand, cycloisomerization of aromatic homo- and bis-homo-propargylic alcohols to benzofurans and isochromenes can be performed using catalytic CpRuCl(PPh3)2 in the presence of an amine as base (Scheme 14) [104]. In a similar manner, benzofurans were also available from homopropargylic aromatic alcohols on using the bifunctional ruthenium catalyst [RuL2Cp(CH3CN)] [PFg] (L=AZARYPHOS, see Scheme 7) [105]. 

These results may be interpreted in terms of the proposed mechanism shown in Scheme 23. Dissociation of Cl from the starting Ru precatalyst is followed by coordination of the alkyne and subsequent rearrangement leads to Ru vinylidene intermediate I. This key intermediate may undergo nucleophilic attack by the pendant amine or amide with concurrent removal of a proton by pyridine to provide the alkenyl Ru species II. Finally, protonolysis by the pyridinium salt formed could provide the final indoles or dihydroisoquinolines, with regeneration of the active catalytic species. A similar mechanistic proposal could be invoked for the preparation of dihydroquinolines from bis-homopropargylic amide. 

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