1,2,6-Oxadiazepine ring

Only one class of fully saturated 1,2,7-oxadiazepine ring system has been reported, although no examples of 1,2,3-oxadiazepine systems are yet known. 

However, the preparation of fully unsaturated monocyclic 1,3,5-oxadiazepine systems had not been reported. Also, since then, several more examples of this oxadiazepine ring system have been... 

An intramolecular diastereoselective cascade cyclization reaction of salen with POCI3, gave rise to a new compound 212 that contains two new stereogenic phosphorus atoms and two new stereogenic carbon atoms in the oxadiazepine ring (14PS226). The polycycHc compound, bis(chlorophosphorylated) decahydro-2,4-di(2-hydroxyphenyl)benzo[chiral carbon atoms in the -position to phosphorus. 

Annulated 1,3,6-Oxadiazepines 3,1,5-Benzoxadiazepines Synthesis by Ring-Closure Reactions... 

Ring expansion has also been observed in the transformation of certain 1-cyano- and 1-phenylisoquinoline 2-oxides to the corresponding benz[/]-l,3-oxazepines,163 of phenyl-substituted quinoxaline 1-oxides to the substituted benz[d]-l,3,6-oxadiazepines,161 164 and of 4-phenylquinazoline 3-oxide (190) to 2-phenylbenz[/]-l,3,5-oxadiazepine (191).165... 

The fused 1,4,5-oxadiazepine 264 was obtained by ring-opening the aziridine ring of 263 with concomitant formation of the seven-membered ring (Scheme 59) <2001J(P1)1518>. 

Monocyclic and fused 1,3,5- and 1,3,6-oxadiazepines are accessible either by one-component cyclization (see Scheme 22), [1+6] cyclocondensation, [3+4] condensation (substitution) reaction, heterocyclic ring rearrangement (see also CHEC(1984) and CHEC-II(1996)), or multicomponent reactions (Scheme 37). The 1,3,5-oxadiazepine heterocyclic ring is also present in iminonucleosides, such as compounds 142 (Scheme 29), which are available via one-component cyclization and [1+6] cyclocondensation reactions. 

The unstable fused 1,2,6-oxadiazepine intermediate 299 has been reported as resulting from 1,7-electrocyclisation of the non-stabilised azomethine ylide 298 on to the nitro group subsequent ring contraction afforded the indazole-JV-oxide 300 [01TL5081]. 

Photolysis of 2-aryl-4-phenylquinazoline 3-oxides caused the oxygen atom to be inserted into the heterocyclic ring. " The 3,4-epoxy intermediate must have undergone a 1,5-sigmatropic shift prior to electrocyclic ring opening to yield 2-aryl-4-phenyl-5,l,3-benzo oxadiazepines [Eq. (13)]. ... 

In a similar reaction, a diazonium ion attached to a diaryl ether attacks a carbon of the other ring to form a doubly fused oxadiazepine. Such reactions have been reviewed [2980]. 

This chapter is organized in a manner similar to Chapter 9.13. Of the ten possible 1,2,4-triheteroepine ting systems, the following five systems, triazepine, oxadiazepine, thiadiazepine, dioxa-zepine, and oxathiazepine ring systems, have been prepared and the other five systems are still unknown. 

Seven-membered Rings with Three Heteroatoms 1,2,4 9.14.3 OXADIAZEPINES... 

The only example of this system that has been prepared is (139). Refluxing jS-arylamino-propiophenone oximes (138) with formaldehyde in ethanol resulted in the condensation with ring closure to give the tetrahydro-l,2,6-oxadiazepines (139) in good yields (Equation (5)) <91MI 914-03). 

Isocyanatobenzoyl chloride (144) reacts with AT-methylhydroxylamine hydrochloride in pyridine, resulting in two competitive cyclization processes to yield two isomeric products, 1,2,4-(145) (73%) and 1,2,6-oxadiazepine (146) (9%) ring systems (Equation (6)) <88IJC(B)840>. 

There are two theoretically possible ring systems several examples of the 1,4,5-oxadiazepine system (89) are known, while the 1,2,5-system (88) has not been prepared. 

Nitrones have been widely exploited in various cycloaddition reactions. Intriguingly, these electrophilic species can also serve as the hydride acceptors. Sun and Xu et al. reported an expeditious access to structurally diverse oxadiazepines 108 via 1,5-hydride shift/cyclization of pyrrolidine- or tetrahydroiso-quinoline-containing nitrones 107 with nitrones as hydride acceptors and AICI3 was exploited as Lewis to promote the cascade process (Scheme 42) [121]. Furthermore, the nitrone 107 could be furnished in situ, which underwent subsequent 1,5-hydride shift, and ring cyclization through a one-pot process to afford 108 in good yields. 

Finally, a few references have appeared in which bidentate compounds have been cyclized using well understood chemistry to produce some novel heterocycles. There are numerous examples of 5- and 6-membered diazaphos-phorus heterocycles but there are far fewer with smaller or larger rings. Dichlorophosphinyl carbamates, prepared from isocyanates, have been cyclized with diamines to afford the novel benzodiazaphosphepin system (395). Oxadiazepins (396) have been prepared by reaction of the amino-oximes with formaldehyde and 1,3,4,6-thiatriazepins (397) were obtained by Moss and Taylor using cyclic thioureas. 

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