Further Insight into the Reactivity of Oxazinones Toward Phosphorus Reagents

Abstract

A series of quinoline derivates has been obtained from the reaction of 3‐phenyl‐2,4‐benzoxazin‐1‐one (1) with alkylidenephosphoranes. With ester ylides 3a,b, the reaction affords hydroxyquinolines 8a,b and new stable phosphorus ylide 9, whereas with keto ylides 3c,d, quinolinones 12a,b, hydroxyindoles 10a,b and benzoazepines 14a,b are obtained. 1 reacts with allyl‐4, methyl‐5a and ethyltriphenylphosphonium bromides 5b in the presence of LiH to afford 2‐hydrophenyloxazolo[1,2‐a]‐ 4‐hydroxyquinoline (16) from the first reaction whereas alkoxyquinolines 21a,b and hydroxyazepines 22a,b are obtained from 5a,b.     

Structural reorganization of (allyl-, benzyl-, and propargylsulfanyl)-substituted 2-aza-1,3,5-trienes in t-BuOK/THF/DMSO: access to rare functionalized 2-thiazolines

Treatment of (allyl-, benzyl-, and propargylsulfanyl)-substituted 2-aza-1,3,5-trienes, which are readily accessible from lithiated methoxyallene, isopropyl isothiocyanate, and allyl, benzyl, or propargyl bromide, respectively, with t-BuOK in THF/DMSO resulted in the unexpected formation of 2-thiazoline derivatives along with seven-membered azaheterocycles [in the case of (allyl- and benzylsulfanyl)-substituted 2-aza-1,3,5-trienes]. An unprecedented structural reorganization of the azatrienes into 2-thiazolines presumably occurs via α-deprotonation of the substituents at the sulfur atom followed by intramolecular [1,5]-cyclization. Deprotonation of the ketimine fragment of the same molecule followed by [1,7]-electrocyclization resulted in azepine ring formation.     

Novel and efficient aqueous phase synthesis of N-substituted azepines via tandem Michael addition and cyclization in the presence of β-cyclodextrin

N-substituted azepines were synthesized for the first time in water under neutral conditions by the reaction of aromatic amines, dimethyl/diethyl acetylene dicarboxylate, 2,5-dimethoxytetrahydrofuran mediated by β-cyclodextrin in high yields. β-Cyclodextrin can be recovered and reused with just a small loss of catalytic activity.     

Synthesis of sulfur-substituted quinolizidines and pyrido[1,2-a]azepines by ring-closing metathesis

Sulfur-substituted quinolizidines and pyrido[1,2-a]azepines (7) can be prepared by ring-closing metathesis (RCM) of 4-(phenylthio)-1,2,5,6-tetrahydropyridin-2-ones (6) bearing terminal alkenyl groups at both N-1 and C-6 positions, which are obtained from 3-(phenylthio)-3-sulfolene (1) in four steps. Some synthetic transformations of 2-(phenylthio)-1,6,9,9a-tetrahydroquinolizin-4-one (7a) and 2-(phenylthio)-1,6,9,10,10a-pentahydropyrido[1,2-a]azepin-4-one (7d) are also reported.