Academic literature on the topic 'Thiophenedicarboxylique-3,5 acide(amino-2 méthyl-4) ester diethyle'

( + )-Pinnatoxin A 3, isolated from the shellfish Pinna muricata, is thought to be a calcium channel activator. A key transformation in the synthesis of 3 reported (J. Am. Chem. Soc . 2008, 130, 3774) by Armen Zakarian, now at the University of California, Santa Barbara, was the diastereoselective Claisen rearrangement of 1 to 2. The alcohol portion of ester 1 was derived from the aldehyde 4, prepared from D-ribose. The absolute configuration of the secondary allylic alcohol was established by chiral amino alcohol catalyzed addition of diethyl zinc to the unsaturated aldehyde 5. The acid portion of the ester 1 was prepared from (S)-citronellic acid, by way of the Evans imide 7. Methylation proceeded with high diasterocontrol, to give 8. Functional group manipulation provided the imide 9. Alkylation then led to 10, again with high diastereocontrol. In each case, care had to be taken in the further processing of the α-chiral acyl oxazolidinones. Direct NaBH4 reduction of 8 delivered the primary alcohol. To prepare the acid 10, the alkylated acyl oxazolidinone was hydrolyzed with alkaline hydrogen peroxide. On exposure of the ester 1 to the enantiomerically-pure base 11, rearrangement proceeded with high diastereocontrol, to give the acid 2. This outcome suggests that deprotonation proceeded to give the single geometric form of the enolate, that was then trapped to give specifically the ketene silyl acetal 12. This elegant approach is dependent on both the ester 1 and the base 11 being enantiomerically pure. The carbocyclic ring of pinnatoxin A 3 was assembled by intramolecular aldol condensation of the dialdehyde 11. This outcome was remarkable, in that 11 is readily epimerizable, and might also be susceptible to β-elimination. Note that the while the diol corresponding to 11 could be readily oxidized to 11 under Swern conditions, attempts to oxidize the corresponding hydroxy aldehyde were not fruitful.

Karl A. Scheidt of Northwestern University described (Organic Lett. 2009, 11, 1651) the oxidation of primary alcohols such as 1 in the presence of an indole 2. The product 3, an active acylating agent, is readily converted to other esters and amides. K. Rajender Reddy of the Indian Institute of Chemical Technology, Hyderabad, developed (Tetrahedron Lett. 2009, 50, 2050) a protocol for the direct oxidation of a primary amine 4 to the corresponding nitrile 5. In the presence of ammonia, the same procedure converted aldehydes and primary alcohols into the nitriles. Several catalytic methods for the oxidation of alcohols to aldehydes and ketones have recently been put forward. René Grée of the Université de Rennes 1 found ( Tetrahedron Lett. 2009, 50, 1493) that ZnBr2 catalyzed the oxidation of alcohols with diethyl azodicarboxylate. Tsutomu Katsuki of Kyushu University designed (Tetrahedron Lett. 2009, 50, 3432) a Ru catalyst for the air oxidation of primary alcohols to aldehydes. Kazuaki Ishihara of Nagoya University showed (J. Am. Chem. Soc. 2009, 131, 251) that 1 mol % of 10 was sufficient to catalyze the oxidation of 6 to 7. With excess oxidant, 7 was carried on cleanly to 11. Nitroxyl radicals such as TEMPO have long been used to catalyze oxidations. Yoshiharu Iwabuchi of Tohoku University developed (J. Org. Chem. 2009, 74, 4619) a simple preparation of 13 , the most efficient such catalyst reported so far. This catalyst should also be useful for the oxidation reported by Professor Iwabuchi (Chem. Commun. 2009, 1739) of primary alcohols and aldehydes to the corresponding carboxylic acids. David S. Forbes of the University of South Alabama prepared (Tetrahedron Lett. 2009, 50, 1855) 16 by combining thioanisole with N-bromosuccinimide. The reagent 16 efficiently sulfenylated active methylene compounds. Jiri Srogl of the Academy of Sciences of the Czech Republic established (Organic Lett. 2009, 11, 843) conditions for the oxidation of primary and secondary amines to aldehydes and ketones. Olga A. Ivanova of Moscow State University demonstrated (Tetrahedron Lett. 2009, 50, 2793) that DMDO 21 could oxidize a sensitive amino cyclopropane such as 20 to the corresponding nitro compound.

It has generally been observed that prospective intramolecular Diels-Alder cycloadditions that would form a γ-lactone are reluctant to proceed. In the course of a synthesis of (±)-neovibsanin B 4, Hiroshi Imagawa and Mugio Nishizawa of Tokushima Bunri University reversed (Organic Lett. 2009, 11, 1253) the usual connectivity and found that the dienyl ester 1 could be induced to cyclize to 3. The solvent 2 improved both the yield and the diastereoselectivity of the cycloaddition. It was not surprising that Johann Mulzer of the University of Vienna could see (Organic Lett. 2009, 11, 1151) no evidence of cyclization on heating the acrylate 5. In contrast, following the lead of Barriault, they found that MgBr2 -tethered cycloaddition of methyl acrylate 7 with the alcohol 6 proceeded smoothly, to give 8, which they carried on to valerenic acid 9. Intramolecular Diels-Alder reactions to form 6,6-systems are often facile. Mohammad Movassaghi of MIT, en route to (-)-himandrine 12, showed (J. Am. Chem. Soc. 2009, 131, 9648) that the tetraene 10 cyclized to 11 at 95°C with 5:1 dr. In this case the solvent was the more typical acetonitrile with 10% diethyl aniline. The intramolecular Diels-Alder reaction is concerted but nonsynchronous (Tetrahedron Lett. 1981, 22, 5141), with β-bond formation preceding α-bond formation. This contributes to the reluctance of 8 to cyclize. In contrast, Henry N. C. Wong of the Chinese University of Hong Kong observed (Angewandte Chem. Int. Ed. 2009, 48, 2351) that the tetraene 13, which is polarity matched, cyclized to 14 spontaneously as soon as it was formed. Functional group conversion completed the synthesis of (±)-pallavicinolide A 15. The transannular Diels-Alder (TADA) reaction can proceed with high diastereocontrol, but the factors directing these cyclizations are not completely understood. In the course of a synthesis of (+)-phomopsidin 18, Masahisa Nakada of Waseda University found (Tetrahedron 2009, 65, 888) that 16 led to 17 with 16:1 dr. In contrast, the triene epimeric to 16 at the silyloxy group cyclized with only 2:1 dr.