Fused azetidinones

The first observation of the uncommon phenomenon of desmotropy in seven-membered heterocycles was reported for the prototropic annular tautomers 128 and 129. These dihydro-4,1-benzothiazepines, which were prepared (via the non-isolated intermediates 130 and 131 from the fused azetidinone 127 on treatment with NaOEt), could be isolated in pure form by column... 

Interestingly, one example is known of a [2 + 2] photocycloaddition from 3-(trifluoromethyl)-quinoxalin-2-one and a ketene, which provides access to fused azetidinones with an angular Irilluoromethyl substituent. ... 

Dihydro-4 f-l,2,5-oxadiazines (21) (see Section 6.15.6.2.3.1) have been used as masked acyl groups for the stereoselective synthesis of 3(a)-(l-hydroxyethyl)-4( )-benzoyl- -lactams (24) (Scheme 2) <88EUP265169>. Condensation of the oxadiazine (21) with (2R,3R)-epoxy-butanoic acid in the presence of dicyclohexylcarbodiimide yields the A(-acyl derivative (22), which on treatment with lithium bis(trimethylsilyl)amide in THE undergoes stereoselective ring closure to the fused azetidinone (23). Hydrolysis with 1 M sulfuric acid in acetone ruptures the oxadiazine ring and forms the -lactam (24). 

Azetidin-2-one, l-benzyl-3,3,4-triphenyl-, 7, 249 Azetidin-2-one, l-(2-bromophenyl)-X-ray crystallography, 7, 247 Azetidin-2-one, 3-carboxy-synthesis, 7, 262 Azetidin-2-one, 3-halo-synthesis, 7, 77 ring contraction, 7, 81-82 Azetidin-2-one, 4-imino-IR spectroscopy, 7, 248 Azetidin-2-one, 1-phenyl-irradiation, 7, 255 Azetidin-2-one, 4-phenyl-reductive ring cleavage, 7, 252 Azetidin-2-one, 4-thio-IR spectroscopy, 7, 248 Azetidinones bicyclic, 7, 348-356 C NMR, 7, 348 H NMR, 7, 348 reactivity, 7, 356-358 spectroscopy, 7, 357 structure, 7, 349 synthesis, 7, 358-359 fused ring... 

The literature on fused-ring azetidines and azetidinones has virtually exploded in the last 15 years. A major factor in the expansion of research in this area has been the discovery... 

Examples of the synthesis of fused-ring azetidines by ring closure onto a preformed azetidine are uncommon, in contrast to approaches used for the preparation of fused ring azetidinones (see Sections 5.12.3, 5.11.4.4 and 5.10.4.3). The l,3-diazabicyclo[3.2.0]hep-tane derivative (48) was prepared (72JOC516) by cyclization with DCC of the carbamoyl-azetidine followed by thermal rearrangement of the intermediate thiazolidinone (Scheme 6). 

The nomenclature used in this section differs from the strictly systematic rules used by Chemical Abstracts to index fused-ring azetidinones, but conforms more to that commonly found in the literature describing the /3-lactam antibiotics. A description of this naming system is given in the introduction (Section 5.12.1). Virtually all of the compounds discussed in this section contain a carboxyl group adjacent to the /3-lactam ring and conform to general structure (49). 

Azetidinones having a ring fused at the N-l/C-4 atoms usually are more susceptible to hydrolysis than those compounds in which the ring fusion is at C-3/C-4. The 2-azabicyclo[2.2.0]hexan-3-one (115) is cleaved with ethanolic HC1 to give ring-opened products (equation 6) (72CB2780). 

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