Intra‐ and Intermolecular Oxa‐Pictet–Spengler Cyclization Strategy for the Enantioselective Synthesis of Deoxy Analogues of (+)‐Nanomycin A Methyl Ester, (+)‐Eleutherin, (+)‐Allo‐Eleutherin, and (+)‐Thysanone

Abstract

Enantioselective synthesis of deoxy analogues of pyranonaphthoquinone antibiotics (+)-nanomycin A methyl ester, (+)-eleutherin, (+)-allo-eleutherin, and (+)-thysanone was achieved in good overall yield with high enantio-and diastereoselectivity from the common intermediate (R)-3-(2,5-dimethoxyphenyl)propane-1,2-diol. The intramolecular oxaPictet-Spengler cyclization of 6-aryl-1,3-dioxolone was de-

Synthesis of Oxacycles Employing the Oxa‐Pictet–Spengler Reaction: Recent Developments and New Prospects

“…Waghmode and co-workers [136] employed an l-prolinecatalyzed asymmetric α-aminooxylation [137] of an aldehyde in conjunction with inter-and intramolecular oxa-PictetSpengler cyclizations for the synthesis of deoxy analogs of several pyrano-naphthoquinones (Figure 3), including (+)-nanaomycin A methyl ester (141), (+)-eleutherin (126), (+)-allo-eleutherin (127), and (+)-thysanone (142), and a formal synthesis of (1R,3S)-thysanone (143). [138] Nanaomycin A (144) was isolated from Streptomyces rosa; [139] it displays significant antitumor activity and inhibitory activity against mycoplasma, fungi, and Grampositive bacteria, being also an inhibitor of platelet aggregation.…”

Oxa-Pictet–Spengler reaction as key step in the synthesis of novel σ receptor ligands with 2-benzopyran structure

“…OEt 2 , TMSOTf, and Bi(OTf) 3 , 38 and can be applied for the stereoselective synthesis of complex natural products. [39][40][41] In order to broaden the relationships between the structure of 1-aminoalkyl substituted 2-benzopyrans and their  1 affinity and selectivity over the  2 subtype, modifications of the side chain in 3-position and the aminoalkyl part of the compounds were envisaged. In order to get access to a side chain bearing an appropriate substituent, the Oxa-Pictet-Spengler reaction using 3-hydroxy-4- …”

A concise and improved synthesis of (+)-eleutherin, (+)-allo-eleutherin and a formal synthesis of (+)-nocardione B

“…Recently, a deoxyeleutherin synthesis has been reported by Waghmode et al based on proline-catalyzed asymmetric a-aminoxylation of aldehydes and oxa-Pictet-Spengler cyclization. 12 Nocardiones 3 and 4 were first synthesized by Mori et al 13 and their absolute configuration was also determined. Racemic syntheses of nocardiones are also known.…”