A new method for synthesis of allenes, including an optically active form, from aldehydes and alkenyl aryl sulfoxides by sulfoxide–metal exchange as the key reaction and an application to a total synthesis of male bean weevil sex attractant

Synthesis and pharmacokinetic properties of novel cPLA2α inhibitors with 1-(carboxyalkylpyrrolyl)-3-aryloxypropan-2-one structure

Indole-5-carboxylic acids with 3-aryloxy-2‑oxopropyl residues in position 1 have been shown to be potent inhibitors of cytosolic phospholipase A₂α (cPLA₂α), an enzyme involved in the formation of pro-inflammatory lipid mediators. Unfortunately, in animal experiments, only very low plasma concentrations could be achieved after peroral administration of this type of compound. Since insufficient metabolic stability was suspected as the cause, structural modifications were made to optimize this property. These included the conversion of the aromatic into an aliphatic carboxylic acid function as well as the rigidification of the lipophilic structural elements. A selected pyrrole-3-propionic acid was tested for its peroral in vivo bioavailability in mice. However, higher plasma concentrations could not be achieved also with this compound. Using the Caco2 cell permeation assay, substances investigated were found to be very good substrates for gastrointestinal efflux transporters, which explains their poor peroral absorption.

Construction of 3-Sulfonyl Naphthalenes via Tandem Reaction of 1,4-Diyn-3-yl Esters with Sodium Sulfinates

Polysubstituted 3-sulfonyl naphthalenes were constructed in good to high yields by AlCl₃-mediated tandem reaction of 1,4-diyn-3-yl esters and sodium sulfinates. This reaction proceeded under mild reaction conditions and tolerated a variety of functional groups. Moreover, the mechanistic studies indicated that the initial formation of allene under DBU from 1,4-diyn-3-yl ester and a sequence of nucleophilic addition of sodium sulfinate, the formation of allene, and intramolecular cyclization might be involved.

Experimental and Computational Studies of the Structure of Sulfonimidoyl Vinyllithiums

tBuCH=C(Li)S(O)(NSO₂ Tol)Ph⋅L (L=2THF, TMEDA) (1⋅L) in THF solution is a monomer with a C-Li bond according to NMR spectroscopy and cryoscopy. It was identified as CIP through the scalar ¹³ C,⁶ Li coupling and ⁶ Li,{¹ H} NOE experiments. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure. ⁶ Li,¹ H FUCOUP and ⁶ Li,¹ H HMQC NMR experiments of 1⋅TMEDA revealed a scalar ⁶ Li,¹ H coupling across the Li-C=C-H bonds. According to the NMR data the π-bond of 1⋅L is polarized by the negative charge of the anionic C atom. tBuCH=C(Li)S(O)(NMe)Ph (2⋅L) is most likely also a monomer with a C-Li bond. According to ⁶ Li,{¹ H} NOE experiments it has a four-membered C-Li-N-S chelate ring structure. ¹³ C NMR spectroscopy showed the C-Li bonds of 1⋅L and 2⋅L to be fluxional. ¹ H NMR spectroscopy and 1D TOCSY experiments of Ph₂ C=C(Li)S(O)(NSO₂ Tol)Ph revealed topomerization of the phenyl groups, which is attributed to a fast positional exchange of the Li atom and the sulfonimidoyl group. The fluxionality of the C-Li bond and the interchange of the Li atom and the sulfonimidoyl group at the anionic C atom of sulfonimidoyl vinyllithiums, which result in a low configurational stability, most likely involve the formation of O,Li and N,Li CIPs through heterolysis of the C-Li bond. Ab initio calculation of MeCH=C(Li)S(O)(NMe)Ph yielded an energy minimum structure with a C-Li bond, a four-membered C-Li-N-S chelate ring and a strongly expanded C=C-Li bond angle. According to calculation of MeCH=C(Li)S(O)(NMe)Ph, [MeCH=CS(O)(NMe)Ph]^- and MeCH=C(H)S(O)(NMe)Ph deprotonation is not accompanied by a shortening of the C-S bond. Ab initio calculation of MeCH=C(Li)S(O)(NSO₂ Me)Ph gave a structure with a C-Li bond and a six-membered C-Li-O-S-N-S chelate ring. ⁶ Li,¹ H NOE experiments and cryoscopy of LiCH₂ S(O)(NSO₂ Tol)Ph (3) revealed a monomeric CIP with a C-Li bond. The CIP has a six-membered C-Li-O-S-N-S chelate ring structure found in polymeric 3 in the crystal.

All-carbon quaternary stereogenic centers in acyclic systems through the creation of several C-C bonds per chemical step

In the past few decades, it has become clear that asymmetric catalysis is one of the most powerful methods for the construction of carbon-carbon as well as carbon-heteroatom bonds in a stereoselective manner. However, when structural complexity increases (i.e., all-carbon quaternary stereogenic center), the difficulty in reaching the desired adducts through asymmetric catalytic reactions leads to a single carbon-carbon bond-forming event per chemical step between two components. Issues of efficiency and convergence should therefore be addressed to avoid extraneous chemical steps. In this Perspective, we present approaches that tackle the stimulating problem of efficiency while answering interesting synthetic challenges. Ideally, if one could create all-carbon quaternary stereogenic centers via the creation of several new carbon-carbon bonds in an acyclic system and in a single-pot operation from simple precursors, it would certainly open new horizons toward solving the synthetic problems. Even more important for any further design, the presence of polyreactive intermediates in synthesis (bismetalated, carbenoid, and oxenoids species) becomes now an indispensable tool, as it creates consecutively the same number of carbon-carbon bonds as in a multi-step process, but in a single-pot operation.

An enantioselective total synthesis of natural antibiotic marasin

Synthetic studies directed toward the allenediyne antibiotic marasin are presented. Different approaches to the installation of the optically active chiral allenediyne motif were explored en route to the synthesis of the natural product. The stereoselectivity for the construction of the chiral allenediyne motif was dependent on not only the reaction employed but also the substrate structure.

Creation of quaternary stereocenters in carbonyl allylation reactions

Despite the advances in stereoselective carbonyl allylation reactions, the creation of quaternary stereocenters in the addition of 3,3'-disubstituted allylmetals to aldehydes is still a challenging issue. This feature article describes the most powerful approaches that have been devised to address this problem.

Expeditious Syntheses of Conjugated Allenyl Esters and Oxazoles through a Cascade Reaction of .ALPHA.-Alkynyl Malonates under Alkaline Conditions

Diethyl alpha-alkynyl-alpha-methoxymalonates (2a--e) were smoothly hydrolyzed and then decarboxylated under alkaline conditions employing 1 N KOH in EtOH to give conjugated allenyl esters (6a--e) in high yields, and similar alkaline treatment of diethyl alpha-alkynyl-alpha-acetylaminomalonates (5a, b, d, e) furnished unexpectedly the oxazoles (7a, b, d, e) having three substituent groups in excellent yields.

Determination of the rate constant for ring opening of an α-cyclopropylvinyl radical

The rate constant for ring opening of the 1-(trans-2-phenylcyclopropyl)ethen-1-yl radical, 4, generated by photolysis of the corresponding vinyl iodide 2, is reported. The value of the rate constant was determined by the tin hydride method and was found to be (1.6+/-0.2)x10(10) s-1, one order of magnitude smaller than the rate constant for rearrangement of the trans-2-phenylcyclopropylcarbinyl radical.

Reaction of magnesium alkylidene carbenoids with lithium alpha-sulfonyl carbanions: a novel synthesis of tri- and tetra-substituted allenes from 1-chlorovinyl p-tolyl sulfoxides and sulfones

Treatment of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from ketones and chloromethyl p-tolyl sulfoxide, with ethylmagnesium chloride or isopropylmagnesium chloride at below -78 degrees C gave magnesium alkylidene carbenoids in about 90% yields. The reaction of the generated carbenoids with lithium alpha-sulfonyl carbanions was found to afford tri- and tetra-substituted allenes. Both cyclic ketones and acyclic ketones were useful in this procedure. However, the 1-chlorovinyl p-tolyl sulfoxides derived from aldehydes gave only rearranged products, acetylenes, under the reaction conditions. The magnesium alkylidene carbenoid derived from an optically active 1-chlorovinyl p-tolyl sulfoxide was treated with lithium alpha-carbanion of 1-naphthyl phenyl sulfone; however, the obtained allene was found to be racemic. The mechanism of this reaction is also discussed.