Regioselective hydrostannation of highly hindered arylalkynes under ortho-directing effects

Abstract

Palladium-catalyzed hydrostannation reactions of ortho-disubstituted arylalkynes were achieved with total stereo-and regioselectivity in THF at room temperature. The regioselectivity was found to be under the control of the ortho-substituents (ortho-directing effects, ODE) and pure -vinyl stannanes are produced in good yields and as single isomers regardless of the substituents' nature. These hydrostannation -products are precursors of choice for the preparation of stereodefined triarylolefins.

Discovery and Hit to Lead Optimization of Novel Combretastatin A-4 Analogues: Dependence of C-Linker Length and Hybridization

“…(v) HCl 1M, 20 °C.Triarylolefin 22 was prepared in five steps from diarylalkyne 25 [77]. We have benefited from the presence of an ortho bromine atom on the trimethoxyphenyl ring of 25 to achieve a regioselective hydrostannation of the triple bond [78][79][80][81][82]. Under this orthodirecting effect (ODE)[79,83], the reaction afforded exclusively -vinyl stannane 26 in a good 92% yield.…”

On the Hydrostannylation of Aryl Propargylic Alcohols and Their Derivatives: Remarkable Differences in Both Regio‐ and Stereoselectivity in Radical‐ and Nonradical‐Mediated Transformations

“…We wondered if these reactions were, in fact, not catalyzed by Pd at all given the very high reactivity that has been observed with the aryl propargylic system in our study. Interestingly, when we used 1‐(2‐methylphenyl)‐2‐phenylacetylene under the conditions presented in Table 3, no reaction occurred, although it did go to completion when the Pd catalyst was added, as was described by Alami and co‐workers11a and Gevorgyan and co‐workers 11b. Clearly, there is something unique about the aryl propargylic alcohol system that leads to this high reactivity.…”

Hydrostannation of Alkynes

“…The hydrostannation provides high selectivity for a single α-isomer, regardless of the electronic nature, coordinating ability or steric hindrance of the ortho substituent (Scheme ). , …”

“…Thus, this ortho-directing effect has been successfully extended to control the regioselectivity of ortho/ortho' diarylalkynes 49 leading to a single constitutional isomer (Scheme 40). 63,79 The regiocontrolled synthesis of alkenylstannane products has been applied to subsequent cross-coupling chemistry to provide selective access to diaryl-and triaryl-substituted olefins. 79 Scheme 39.…”

“…Furthermore, exclusive α-regioselectivity is also observed with sterically congested ortho,ortho′-disubstituted terminal aryl alkynes (Scheme 26). 63 Hydrostannation of heteroaromatic alkynes is poorly documented with only the α-stannylcupration of 2-ethynylpyridine in the presence of water, (SnMe 3 ) 2 , PtBu 3 , and Cu(OAc) 2 . 64 During the synthesis of Scalaridine A, a symmetrical bis-indole isolated from the marine sponge Scalarispongia sp., 65 it was reported that hydrostannation of 3,5-diethynylpyridine 66 was achieved under Pd-catalysis with a total α-selectivity (Scheme 27).…”