Lactams, preparation from azides

A third approach to 3-amino-/3-lactams is by Curtius rearrangement of the corresponding acyl azides. These are readily prepared from r-butyl carbazides, available via photochemical ring contraction of 3-diazopyrrolidine-2,4-diones in the presence of f-butyl carbazate (c/. Section 5.09.3.3.2). Thus treatment of (201) with trifluoroacetic acid followed by diazotiz-ation gives the acyl azide (202) which, in thermolysis in benzene and subsequent interception of the resulting isocyanate with r-butanol, yields the protected 3-amino-/3-lactam (203) (73JCS(P1)2907). 

The asymmetric syntheses of carnosadine (lS,2S)-74 [101] and of its protected derivatives as conformationally constrained surrogates for arginine have also been reported [102]. Different 2-substituted 1-aminocyclopropanecarboxylic acids have also been prepared by azidation of optically active 2-chloro-2-cyclo-propylideneacetates [103] and from the cyclopropanation of chiral bicyclic lactams [104]. 

The use of acylnitiene cyclizations in the synthesis of diteipene alkaloids goes back to the early 1960s, and although much of the early work has been reviewed, selected examples are included here. The acyl azide (19), readily prepared from podocarpic acid, was irradiated to give the 8-lactam (20 20%), which has the azabicyclononane ring system of the diteipene alkaloids such as atisine. ... 

The limitations of this approach can be seen in the reaction of a saturated solution of ammonia in 90% ethanol with ethyl bromide in a 16 1 molar ratio, under which conditions the yield of primary amine was 34.2% (at a 1 1 ratio the yield was 11.3%). Alkyl amines can be one type of substrate that does give reasonable yields of primary amine (provided a large excess of NH3 is used) are a-halo acids, which are converted to amino acids. A-Chloromethyl lactams also react with amines to give good yields to the A-aminomethyl lactam. Primary amines can be prepared from alkyl halides by 10-43, followed by reduction of the azide (19-32), or by the Gabriel synthesis (10-41). 

Regioselective Beckmann rearrangements were used as key steps in the synthesis of phosphonoalkyl azepinones (Scheme 36) [43b] and in a formal total synthesis of the protein kinase C inhibitor balanol (Scheme 37) the optically active azide 197 derived from cyclohexadiene mono-oxide was converted into ketone 198 in several steps. After preparation of the oxime tosylates 199 (2.3 1 mixture), a Lewis acid mediated regioselective Beckmann rearrangement gave the lactams 200 and 201 in 66% and 9% yield, respectively. Lactam 201 underwent a 3-e im-ination to give additional 200, which served as a key intermediate in a balanol precursor synthesis (Scheme 37) [43 cj. 

A study of ketene A, O-acetals has shown that such compounds derived from lactam acetals may be used in the preparation of larger heterocyclic systems via reaction with a 1,3-dipolar species, the initial cycloadducts stabilizing their structures by aromatization. Pyrrolo[2,3-i/]-l,2,3-triazole derivatives, however, do not undergo such elimination reactions and stable cycloadducts may be obtained. Thus, the lactam acetals (133) give the ketene A,0-acetals (134), which on reaction with p-nitrophenyl azide yield substituted pyrrolo[2,3-d]-l,2,3-triazole derivatives (135) <86CB359l>. 

Dehydration. This reagent is useful for synthesis of acyl azides from carboxylic acids, NaCN, and pyridine, with tetrabutylammomum bromide as catalyst (75-95% yield). In combination with pyridine, it effects dehydration of oximes to nitriles in 80-90% yield, P-Lactams can be prepared directly in 40-75 )t yield from carboxylic acids and imines with the reagent (1 equiv,) and triethylamine (excess). In general, a mixture of cis- and rra/j5-azetidinones is formed. 

Oximes, Amides, Amidoximes, Lactams, Hydroxamic Chlorides, Imide Chlorides, and Dichloroketcmes. The preparation of 1,5-penta-methylenetetrazole from cyclohexanoneoxime and sodium azide in the... 

Esterification at room temp, with tetrachloroaluminic acid ether complex has been described The alcoholysis of a-mono-alkylacetoacetates to the corresponding esters and alkyl acetates has been accomplished with excellent yields A new modification of the Curtius degradation avoids the prepn. of acid chlorides by using in their place carboxylic alkoxyformic anhydrides intermediates well-known in peptide chemistry. Among recent developments in this latter field are the use of mixed anhydrides prepared with diphenylketene an improved peptide synthesis via azides prepared with nitrosyl chloride or butyl nitrite instead of aq. sodium nitrite and a rapid synthesis directly from acid hydrazides with N-bromosuccinimide Oligopeptides and /5-lactams have been synthesized from simple starting materials and isonitriles,... 

---