Cycloadditionen von 1,3,4‐Oxadiazin‐6‐onen (4,5‐Diaza‐α‐pyronen), 9. 6‐Oxo‐5‐phenyl‐1,3,4‐oxadiazin‐2‐carbonsäure‐methylester — Synthese und Reaktionen mit Norbornen, Norbornadien, Cyclopropenen, Cyclobuten und Benzvalen

Abstract

Enol lactones, a$-unsaturated ~ Cycloadditions of 1.3.4-Oxadiazin-6-ones (4.5-Diaza-a-pyrones). 9 'I. -Methyl 6-0xo-5-phenyl-1,3,4-oxadiazin-2-carboxylate -Synthesis and Reactions with Norbornene, Norbornadiene. Cyclopropenes, Cyclobutene. and Benzvalene Methyl 6-oxo-5-phenyl-l,3,4-oxadiazin-2-carboxylate (7) was pene, and cyclobutene were converted by 7 mainly into the prepared by treatment of hydrazone 6 with dicyclohexylcar-oxepin derivatives 15, 17, 18, and the oxocin derivative 19, bodiimide. The reactions of 7 with norbornene and norbor-respectively. Benzvalene and 7 provided the tetracynadiene afforded the Diels-Alder adducts 8 and 9, respectively, clo[3.3.0.02~a.04~6]octan~ne 21. In these reactions, small quantiwhich decomposed in solution at 20°C to give mainly the y-ties of p-lactones were formed, too, which together with the oxoketenes 10 and 12 and small amounts of the p-lactones 11 p-lactones 11 and 13 give evidence for the dihydropyryliumand 13, respectively. The stable y-oxoketenes 10, 12, and the olates 24 as intermediates in the thermal denitrogenation of bis(y-oxoketene) 14 were obtained directly from solutions of 7 the Diels-Alder adducts of 7, e.g. A. 6-Oxo-5-phenyl-l,3,4-oxadiazin-2-carbonsauremethylester (7) Der Weg zu 7 ist dem von Steglich et al.3b,4) Chem.

Total Synthesis of (+)-Fendleridine (Aspidoalbidine) and (+)-1-Acetylaspidoalbidine

“…The required 1,3,4-oxadiazole 5 bearing the tethered indole dipolarophile was prepared from 1-benzyltryptamine ( 7 , Scheme ) in a three-step sequence. Treatment of 7 with 1,1-carbonyldiimidazole (CDI) afforded urea 8 (97%), which was reacted with methyl oxalyl hydrazide 9 to provide 10 . Dehydration of 10 by treatment of TsCl and Et 3 N afforded the oxadiazole 5 (81% for two steps).…”

Total Synthesis of (−)- and ent-(+)-Vindoline and Related Alkaloids

“…The starting 2-amino-1,3,4-oxadiazole 16 for the synthesis of 4 − 7 was prepared from N -methyl tryptamine ( 12 , Scheme ). Treatment of 12 with carbonyldiimidazole afforded 13 (89%) that was converted to the oxadiazole precursor 15 (93%) by treatment with methyl oxalylhydrazide ( 14 ) in the presence of HOAc. Cyclization of 15 to form the corresponding oxadiazole 16 was mediated by TsCl and Et 3 N (83%).…”

The Application of Cyclobutane Derivatives in Organic Synthesis

“…Under selective extrusion of nitrogen, these compounds represent interesting building blocks in lactone syntheses. Reacting oxadiazinone 543 with cyclobutene, Christl et al obtained the desired cycloaddition product 5,8-dihydro-8-oxo-7-phenyl-4 H- oxocine-2-carboxylic acid methyl ester ( 544 ) in 59% yield ) …”