158362-89-1Relevant articles and documents
Competition of Mechanisms in Nucleophilic Substitution of Vinyl Halides. An Unequivocal Example of the Vinylic SRN1 Route
Galli, Carlo,Gentili, Patrizia,Rappoport, Zvi
, p. 6786 - 6795 (1994)
In a search for an unambiguous example of the vinylic SRN1 route, several vinyl bromides and iodides were reacted mostly with (-)CH2COCMe3, and sometimes with (-)CH2COPh, (-)CH(Me)COEt, and (EtO)2PO(-) ions, under Fe(2+)- or photostimulation in Me2SO.Vinyl halides having vinylic hydrogens, such as β-bromostyrene, gave acetylenic products, e.g., phenylacetylene or a tertiary PhCC-substituted alcohol, whereas vinyl halides with allylic hydrogens, such as Me2C=C(I)CHMe2, gave a substituted allene.Reduction products of the halogen, as well as substitution and rearranged substitution products, were also formed.The operation of ionic elimination-addition routes accounts for formation of most of the products, while the reduction products arise from an intermediate vinyl radical.Ph2C=C(Br)Ph (20) and Me2C=C(Br)Ph (25) gave both substitution and reduction products, but Me2C=C(Br)-t-Bu (23) gave only a reduction product.Formation of substitution products from the conjugated 20 and 25 was ascribed to a reaction via a vinylic SRN1 route, while lack of substitution in 23 is related to its nonconjugated system and to the consequent higher energy that the radical anion of the substitution product would have.The one here reported seems to be the first case of an exclusive genuine vinylic SRN1 process.
The suzuki coupling reaction in the stereocontrolled synthesis of 9-cis-retinoic acid and its ring-demethylated analogues
Pazos,Iglesias,De Lera
, p. 8483 - 8489 (2007/10/03)
The thallium-accelerated Suzuki coupling reaction of tetraenyl iodide 19 and cyclohexenyl boronate 18 afforded ethyl 9-cis-retinoate (12) in high yield. Both coupling partners of the Suzuki reaction are better reacted immediately after generation from their precursors, tetraenylstannane 10 and cyclohexenyl iodide 13. The geometrically homogeneous tetraenylstannane 10, comprising the polyenic side chain of ethyl 9-cis-retinoate and its ring-demethylated analogues, was synthesized by a stereoselective Horner - Wadsworth - Emmons reaction. On the other hand, easily available cyclohexanones are ideal starting materials for preparation of the cyclohexenyl boronates required for the synthesis of the ring-modified 9-cis-retinoic acid analogues. For hindered cyclohexanones, hydrazones were converted to cyclohexenyl iodides. Iodine - lithium exchange and trapping with B(OMe)3 then afforded the cyclohexenyl boronates. If the precursor cyclohexanone has secondary carbons, the alkenyllithium species was conveniently formed by elimination of the C,N-dilithiated intermediate obtained upon treating the trisylhydrazone with n-BuLi (Shapiro reaction). None of the above procedures allowed the generation of the more substituted organolithium from 2-methylcyclohexanone. However, the alternative Stille cross-coupling of 34 and 10 afforded 9-cis-1,1-bisdemethylretinoic acid 7. Both Suzuki and Stille coupling reactions took place under mild conditions, and the preservation of the retinoid side-chain geometry was therefore secured.
