Stereoselective synthesis of 4-hydroxy-2-phenylproline framework

Highly diastereoselective (>20:1) bromo-lactonization of N-sulfonyl-2-allyl-2-phenylglycine methyl ester (11) was observed. Successive treatment of the chiral lactone with MeONa gave the desired (2S,4R)-4-hydroxy-2-phenylproline derivative in high yield without erosion of the diastereoselectivity. The starting chiral non-racemic compound (5) was prepared from the racemic 2-phenylglycine using a classical kinetic resolution (crystallization), an asymmetric phase transfer alkylation, and an enzyme-catalyzed kinetic resolution.     

A convenient synthesis of enantiopure (4aS,7aR)-1,4,4a,7a-tetrahydrocyclopenta[c]pyran-3,7-dione

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Total synthesis of (−)-funebrine via Au-catalyzed regio- and stereoselective γ-butyrolactonization of allenylsilane

The stereoselective total synthesis of (−)-funebrine from 2-butyn-1-ol was described. The crucial steps in the synthesis involved the stereoselective enolate Claisen rearrangement of the (S)-α-acyloxy-α-alkynylsilane 8, the Au-catalyzed regio- and stereoselective lactonization of the allenylsilane 7, and the Paal-Knorr pyrrole condensation using an unsymmetrical 1,4-diketone 4b.     

Thermal degradation behavior of polyamides having 2- and 4-hydroxycinnamic acid dimer components

Two new types of polyamides having anti head-to-tail hydroxycinnamic acid dimer component in the main chain were synthesized. Their thermal degradation behavior was investigated by TG-DSC analysis in comparison with those of their model compounds and the polyamides derived from anti head-to-head coumarin dimer. The key reactions in the thermal degradation were clarified to be lactonization and cyclic imide formation. The polyamide, derived from 4-hydroxycinnamic acid dimer and hexamethylenediamine, showed good heat stability. © 1993 John Wiley & Sons, Inc.     

A stereoselective approach for the total synthesis of (5R,7R,9R)-7,9-dihydroxy-5-decanolide#

A stereoselective approach for the total synthesis of lactone (5R,7R,9R)-7,9-dihydroxy-5-decanolide is described. The sequence of synthetic reactions involves a Keck asymmetric allylation, diastereoselective iodo-carbonate cyclization, regioselective ring-opening reaction, oxidative lactonization.     

Asymmetric synthesis of (–)-leiocarpin A via (–)-(S)-goniothalamin employing Julia–Kocienski olefination

A concise and enantioselective syntheses of antileukemic natural products such as (–)-(S)-goniothalamin and (–)-leiocarpin A has been accomplished in excellent yields. By employing reported conditions on suitable substrates via Julia–Kocienski olefination, intramolecular lactonization, and subsequently dehydroxylative olefination, (–)-(S)-goniothalamin was synthesized. Then Sharpless asymmetric dihydroxylation–intramolecular Michael addition on (–)-(S)-goniothalamin provided (–)-leiocarpin A.     

Evaluation of the Efficiency of the Macrolactonization Using MNBA in the Synthesis of Erythromycin A Aglycon

Various intermediates for the synthesis of erythronolide A, an aglycon of erythromycin A, are prepared from the corresponding seco‐acids using 2‐methyl‐6‐nitrobenzoic anhydride (MNBA) in the presence of 4‐(dimethylamino)pyridine (DMAP) with or without triethylamine. The efficiency of the MNBA lactonization is assessed by studying this method and comparing the results with those of the other established macrocyclization protocols. It has been finally concluded that (i) the conformationally appropriate substrate for the monomeric cyclization gave the desired lactone in excellent yield under mild reaction conditions in the presence of MNBA and DMAP, (ii) the highly‐strained substrate for the cyclization also afforded the monomeric lactone in relatively good yield at 100°C in toluene, and (iii) the seco‐acid having stable linear conformation, which preferred dimerizing more than forming the monomeric lactone, provided the corresponding diolide in high yield with the constant ratio of the monomer to dimeric lactone (approximately 1/5). © 2009 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 9: 305–320; 2009: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.200900017     

Regioselective Baeyer-Villiger lactonization of 2-substituted pyrrolidin-4-one. Synthesis of statine

Nine 2-substituted pyrrolidin-4-ones 4a-i were obtained via a series of functional group transformation of known prolinol 5 by facile six kinds of methodologies. The target structure of 1,3-amino alcohols 2a-i was constructed in the regioselective Baeyer-Villiger lactonization of ketones 4a-i and reduction of the resulting 4-substituted tetrahydro-1,3-oxazin-6-ones 3a-i. A new and straightforward synthesis of (3S,4S)-statine (6) has been established starting from trans-(2S,4R)-4-hydroxyproline (1).