Esta es la versión de autor del artículo publicado en: This is an author produced version of a paper published in: El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription Mo(CO) 6 from 1.0 equiv (43% conversion, entry 1 in Table 149 1) to 0.5 equiv (67% conversion, entry 2 in 199 This good trans-diastereoselectivity is remarkable, revealing a 200 marked preference for C−H activation of the pro-S methyl 201 group of (+)-3.23e Importantly, the major (−)-trans-9 202 diastereomer could be isolated in 75% yield with no appreciable 203 loss of enantiopurity (97% ee) upon standard chromatography. 204Although the structure of the bimetallic complex of γ-205 cyclopalladation of tert-leucine derivative (+)-1 (complex A) 206 strongly suggested that the NH−SO 2 Py directing group is 207 crucial for this transformation, we were interested in confirming 208 this issue by screening other potentially coordinating N-209 protecting groups. For this purpose, a set of L-valine derivatives 210 (substrates 4−8) were examined in the carbonylation reaction 211 under the optimized conditions, and the results are summarized 212 in Table 2. While L-valine methyl ester hydrochloride 213 decomposed under the reaction conditions (entry 2 in Table 214 2), the NH-Ts derivative 5 and the NH-(2-thienyl)sulfonyl 215 derivative 6 were recovered unaltered without detecting any 216 carbonylation product (entries 3 and 4, respectively, in Table 217 2). The reaction of the (8-quinolyl)sulfonyl and (2-pyridyl)-218 carbonyl derivatives (7 and 8, respectively) led to a complex 219 mixture of products in low conversion (<10%) (entries 5 and 6 220 in Table 2). Interestingly, the lack of reaction efficiency 87 (75) e 5.7:1 (9) 9 7 2 −(4)a Reaction conditions are identical to those given in Table 1 This method was extended to β-amino acid derivatives, as 260 exemplified by the clean cyclocarbonylation of β-amino ester 261 (±)-19, affording the product (±)-20 as a separable 3.8:1 262 mixture of trans/cis diastereoisomers in good overall yield 263 (76%). 264Extension of the Method to Simple Aliphatic Amines. 265 The broad substrate scope displayed by this reaction with α-266 amino acid derivatives prompted us to explore the extension of 267 this method to simple aliphatic amine derivatives. We first 268 tested if compound (−)-21, analogue to tert-leucine derivative 269 1 but lacking the methyl ester moiety, could undergo γ-270 cyclometalation. The stoichiometric reaction of (−)-21 with 271 Pd(OAc) 2 (1.0 equiv) in acetonitrile at 60°C for 3.5 h, cleanly 272 provided, after simple recrystallization, the expected bimetallic 273 complex B in 91% yield (unambiguously determined by singles3 274 crystal X-ray diffraction (XRD) analysis; see Scheme 3), which 275 presents an analogous structure to complex A. This result demonstrated that the ester group at the α-277 position of the previously studied α-amino ester derivatives was 278 not essential for the C−H activation step. Fu...

Good to excellent reactivity and regiocontrol have been achieved in the Cu(I)-catalyzed borylation of dialkyl internal alkynes with bis(pinacolato)diboron. The presence of a propargylic polar group (OH, OR, SAr, SO(2)Ar, or NHTs), in combination with PCy(3) as ligand, allowed maximizing the reactivity and site-selectivity (β to the propargylic function). DFT calculations suggest a subtle orbitalic influence from the propargylic group, matched with ligand and substrate size effects, as key factors involved in the high β-selectivity. The vinylboronates allowed the stereoselective synthesis of trisubstituted olefins, while allylic substitution of the SO(2)Py group without affecting the boronate group provided access to formal hydroboration products of unbiased dialkylalkynes.

Switchable site-selectivity through catalyst control is achieved in the direct functionalization of picolinamides that contain two distinct C–H sites to construct diverse scaffolds from the same starting material.

A general and efficient method for the rhodium-catalyzed enantioselective catalytic conjugate addition of organoboronic acids to alpha,beta-unsaturated sulfones is described. The success of the process relies on the use of alpha,beta-unsaturated 2-pyridyl sulfones as key metal-coordinating substrates; typical sulfones such as vinyl phenyl sulfones are inert under the reaction conditions. Among a variety of chiral ligands, Chiraphos provided the best asymmetric induction. This rhodium [Rh(acac)(C2H4)2]/Chiraphos catalyst system has a broad scope, being applicable to the addition of both aryl and alkenyl boronic acids to cis and trans alpha,beta-unsaturated 2-pyridyl sulfones. In most cases, especially in the addition of aryl boronic acids, the reactions take place cleanly and with high enantioselectivity, affording chiral beta-substituted 2-pyridyl sulfones in good yields and enantioselectivities (70-92% ee). The sense and magnitude of this enantioselectivity have been studied by DFT theoretical calculations of the aryl-rhodium insertion step. These calculations strongly support the formation of a five-membered pyridyl-rhodium chelated species as the most stable complex after the insertion into the C=C bond. These highly enantioenriched chiral sulfones are very appealing building blocks in enantioselective synthesis. For instance, the straightforward elimination of the 2-pyridylsulfonyl group by either Julia-Kociensky olefination or alkylation/desulfonylation sequences provides a variety of functionalized chiral compounds, such as allylic substituted alkenes or beta-substituted ketones and esters.

The glycosylation of 1,2‐trans‐diequatorial diols derived from tetrabenzoylated and tetrabenzylated D‐ and L‐chiro‐inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The easily available vinyl sulfone 3 showed great potential for new applications in several fields such as organic synthesis and bioconjugate formation. This was demonstrated by performing a systematic assessment of its reactivity in Michael, radical, and cycloaddition reactions. Heteroaryl vinyl sulfone 3 presented excellent output in terms of reactivity and selectivity, proving superior to phenyl vinyl sulfone 1 and with clear advantages over bis-sulfone 2. This behavior might be due to the conformational and orbital control exerted by the tetrazole unit according to DFT calculations. Moreover, some alternative transformations to the Julia-Kocienski olefination on the obtained products are also described.

A silver-catalyzed 1,3-dipolar cycloaddition of fluorinated azomethine ylides and activated olefins is reported. The reaction offers a straightforward and atom-economical procedure for the preparation of fluorinated pyrrolidines. Broad scope and high levels of diastereoselectivity have been achieved simply by using AgOAc/PPh3 as the catalyst system. The high efficiency of the cycloaddition relies on the presence of a metal-coordinating group on the imine moiety, such as an ester or heteroaryl group. The asymmetric version of the cycloaddition has been developed by using Taniaphos as a chiral ligand.

Dedicated to Professor Josep M. Ribó on the occasion of his 70th birthdayThe 1,3-dipolar cycloaddition of azomethine ylides with alkenes is one of the most powerful and convergent methods for the stereoselective synthesis of pyrrolidines, [1] a heterocyclic moiety widely present in the structure of natural products, pharmaceuticals [2] and chiral ligands. [3] Improving the overall chemical and stereochemical efficiency of this reaction, pioneered by Grigg with stoichiometric metal chiral complexes, [4] a great effort has been devoted in recent years in the development of catalytic asymmetric protocols. In this field a wide variety of outstanding chiral complex catalysts have been reported, [5] mainly Ag I , [5f,g,j,m,q-s] Cu I[5e,h,i,k,l,o,t-w] and Cu II[5d] catalysts, but also Zn II , [5x] Ni II[5n] and Ca II[5p] complexes. In addition, several organocatalytic asymmetric methods have been also developed in the last few years. [6] Concerning the scope of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides, although there is an ample tolerance with regard to the nature of the dipolarophile (i.e., a,b-unsaturated esters, maleimides, a,b-unsaturated nitriles, enones, enals, nitroalkenes, vinyl sulfones and fullerene), the structural variety at the azomethine dipole is much more limited. By far most catalytic asymmetric versions reported to date are based on the use of a-iminocarbonyl substrates, specifically a-iminoesters. The great effectiveness of a-iminoesters as dipole precursors relies on the enhanced acidity of the a-position and the formation of a robust five-membered, N,O-bidentate-metalated, azomethine ylide, which facilitates the asymmetric induction from the chiral ligand. The inherent limitation of this strategy is the restricted structural versatility with regard to the substitution at C2, always providing pyrrolidines with a C2 carboxylate ester substitution.To access other types of substituted pyrrolidines, a-iminonitrile precursors are very appealing, since in the resulting 2-cyanopyrrolidines [7] the cyano group could further act as leaving group allowing its formal substitution by hydrogen or by a carbon nucleophile, [8] and thus leading to a wider variety of substituted pyrrolidines. Two decades ago Kane-A C H T U N G T R E N N U N G masa, Tsuge et al. reported the non-enantioselective thermal [9] and LDA-promoted (LDA = lithium diisopropyl- A C H T U N G T R E N N U N G amide)[10] cycloaddition of alkyl-substituted a-iminonitriles with electron-deficient dipolarophiles, but the catalytic asymmetric version of this process remained to be developed. We describe herein the first catalytic asymmetric procedure for the 1,3-dipolar cycloaddition of a-iminonitriles, as well as some synthetic applications and a DFT theoretical study on the presumed nature of the metalated 1,3-dipole.To evaluate the viability of a-iminonitriles as dipole precursors in catalytic asymmetric 1,3-dipolar cycloadditions, we first studied the reaction of N-benzylidenaminoacetonitrile (1) with meth...