Palladium catalysis intramolecular

Several examples of transition metal catalysis for the synthesis of piperidines appeared this year. Palladium catalyzed intramolecular urethane cyclization onto an unactivated allylic alcohol was described as the key step in the stereoselective synthesis of the azasugar 1-deoxymannojirimycin . A new synthetic entry into the 2-azabicyclo[3.3.1]nonane framework was accomplished through a palladium mediated intramolecular coupling of amine tethered vinyl halides and ketone enolates in moderate yields . A palladium catalyzed decarboxylative carbonylation of 5-vinyl... 

The intramolecular arylation of sp3 C-H bonds is observed in the reaction of l-/ r/-butyl-2-iodobenzene under palladium catalysis (Equation (71)) 94 94a 94b The oxidative addition of Arl to Pd(0) gives an ArPdl species, which undergoes the electrophilic substitution at the tert-butyl group to afford the palladacycle. To this palladacycle, another molecule of Arl oxidatively adds, giving the Pd(iv) complex. 

A few synthetic applications of palladium catalysis appeared this year. The palladium-catalyzed cyclization of amino allenes 58 occurs with coupling of aryl iodides or vinyl triflates at the 3-position <990L717, 99SL324>. The cyclization can also proceed by the exo-trig pathway, but under suitable reaction conditions the piperidine 59 is prepared selectively. The intramolecular cyclization of amines onto N-allylbenzotriazoles similarly affords piperidines <99JOC6066>. 

Five-membered ring closures have been observed when o-halostyrene derivatives such as 113 were coupled with alkenes under palladium catalysis. Apparently, an intramolecular carbopalladation with S-exo-trig ring closure to give 114-R can favorably compete with / -hydride elimination in the first-formed intermediate to yield 115-R This reaction mode for the halostyrene is observed especially under Jeffery conditions, when the alkene is ethene or propene (Scheme 31). Under the same conditions, however, < -dibromobenzene gives very high yields of o-dialkenylbenzene derivatives (see Scheme 2). ... 

Under palladium catalysis, the < -iodoallenylbenzene 146 first undergoes an intermolecular carbopalladation of the double bond in the added norbornene 116, and only then follows an intramolecular carbopalladation of the allene moiety in 146 ensuing /3-hydride elimination finally provides the tricyclic compound 147 (Scheme 37)7 ... 

The intramolecular palladium catalyzed ring closure of the tetrahydro-isoquinoline derivative depicted in 8.41. led to the formation of the aporphine derivative in good yield, which was then converted into racemic aporphine in three steps. In the ring closing step 20 mol% palladium acetate and 40 mol% tricyclohexylphosphine were used as catalyst. The removal of the hydroxyl group was also achieved by palladium catalysis through its conversion to triflate and the subsequent reduction with ammonium formate in the presence of palladium acetate and dppf.53... 

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

The desymmetrization of dicarbonate 206 was initiated by the addition of one equivalent of N-(3-butenyl) nosylamide 207 under palladium catalysis in the presence of Trost s chiral diphosphine ligand 205. When the first allylic substitution was completed, the reaction was warmed and the resulting intermediate 208 was treated in situ with one equivalent of a second nosylamide 209. Product 210 resulting from this double substitution reaction was submitted to a tandem intramolecular ROM/RCM to furnish key precursor 211, which was engaged in the final cyc-lization step by the reduction of the double bonds, followed by the HCl-promoted domino deprotection of the acetal and aminal formation. 

Stannaries have become prominent in multifunctional anchoring groups. A polymer-bound tin hydride 41 has been used to hydrostannylate alkynes under the action of palladium-catalysis to give polymer-bound alkenylstannanes 42. These alkenyl stannanes have been employed in intermolecular [45] and intramolecular Stille reactions [46]. Alkenylstannanes can also undergo protonation to give alkenes 44 in a traceless fashion. This linker is therefore multifunctional (Scheme 6.1.12). 

Intramolecular variants of the Alder-ene type couplings between alkynes and alkenes have been extensively explored by means of palladium catalysis [73]. Recently, such a cycloisomerization of enynes was also accomplished with ruthenium catalysis (Scheme 4.32) [74]. 

During (he last few years, a novel Pd(O)-catalyzed method for C-N bond formation from amines and aryl halides has emerged largely due to contributions from the Buchwald and Hartwig groups [120, 121]. In one application, an intramolecular C-N bond linkage was realized using classic palladium catalysis condition in Buchwald s synthesis of tetrahydropyrroloquinoline... 

Another instance for this linker class is the safety-catch linker by Lyttle, which was developed for the synthesis of nucleic acids on solid supports [62]. Starting from a resin carrying an Alloc-protected amino group fragment, conventional phosphoramidite chemistry was carried out to build up the desired immobilized nucleotide 57. Removal of the Alloc group via palladium catalysis under neutral conditions produces a polymer-bound intermediate 58 with a free amino functionality that can intramolecularly attack activated phosphonates and liberate the nucleotide 59 from the solid support (Scheme 16.14). More examples of safety-catch linkers that use the deprotection of an N-functionality as the activation step are listed in Table 16.1 (resins 61-65) [63-68]. 

Biaryl structures are found in a wide range of important compounds, including natural products and organic functional materials [8,80,81]. One of the most common and useful methods for preparing biaryls is the palladium-catalyzed coupling of aryl halides with arylmetals (Scheme 1, mechanism A). On the other hand, aryl halides have been known to couple directly with aromatic compounds as formal nucleophiles under palladium catalysis. While the intramolecular cases are particularly effective, certain functionalized aromatic compounds such as phenols and aromatic carbonyl compounds, as well as... 

---