Ring expansion with isocyanates

Without additional reagents Ring expansion with isocyanates l,3,5-Triaza-2-boracyclooctan-4-ones from 1,3,2-diazaboracyclohexanes... 

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

The same ring expansion occurs on the reaction of 3,3-di-n-propyl-diaziridine with two molecules of phenyl isocyanate [Eq. (40)]. ... 

The azirine 1 reacts with thiobenzoyl isocyanate to give the Diels-Alder adduct 2. which at 80CC undergoes ring expansion to the thiadiazepinone 3, the only known representative of this ring system.327... 

The 2-vinylpyrrolidines can undergo a Pd(0)-catalyzed ring expansion upon treating them with aryl isocyanates (Equation 15) <2003JOC3439>. 

Li et al. used a similar rearrangement to synthesize 1,4-oxazepine 252, but instead of antimony pentachloride, tetrafluoroboric acid was employed as the acid. In the solution of bicyclic geminal arylazo isocyanate 250 in diethyl ether, a solution of tetrafluoroboric acid was added to form triazolium tetrafluoroborate salt 251. The rearrangement of 251 occurred quickly under mild conditions with ring expansion to yield the tricyclic 252 in less than 5 min. The isomeric form 253 is not observed (Scheme 45) <2004SC1691>. 

Beckert et al. have reported a ring expansion as well as an N-acylation reaction under mild conditions when 1,2-diazetines 112 were treated with isothiocyanate and isocyanate, respectively <2005H(65)1311>. When an acyl halide is used, N-acylation was observed to give 114 which underwent thermal rearrangement to furnish 4//-l,3,4-oxadi-azines 115 (Scheme 12) (see Section 2.13.6.2) <2006S514>. 

Enantiomerically pure N,N-disubstituted imidazolidine-2-one-4-carboxylates 332 can also be obtained in a one-step, simple, and highly efficient manner using a Lewis acid-catalyzed ring-expansion reaction of commercially available chiral aziridines with isocyanates. These reactions proceed both regio- and stereospecifically with retention of the configuration at the C-2 carbon of the chiral aziridines <2005CC3062>. The C(2)-N bond of the aziridine... 

When the thiazine ester (708) was treated with an isocyanate such as (709), an imidazo[5,l-c][l,4]thiazine (710) was produced (8UAP8161384). Treatment of certain penicillin sulfoxide esters (711) with ethoxycarbonyl isocyanate results in a ring expansion of both rings to afford an imidazo[5,l-c][l,4]thiazine (712) (81JOC3026). 

Ring expansion of lactones by reaction of the latter with lithiated chloromethyl phenyl sulfoxide with subsequent treatment with KH and then f-BuLi is a mechanistically intriguing transformation. Episulfone is readily deprotonated. Tris(trimethylsilyl)episulfone has been obtained. A convenient synthesis of trimethylsilylmethyl isocyanate is by Hthiation of... 

A ring expansion reaction of (274) with phenyl isocyanate has been reported to afford (275) (Equation (62)) <78JOM(i54)C3>. 

The cephem derivative (454) reacted with chlorosulfonyl isocyanate to undergo -lactam ring expansion, resulting in (455) (Equation (111)) <78JCS(P1)817>. 

The isoxazolinone (505) undergoes ring-expansion to the 1,3-oxazinone (506) in the reaction with phenyl isocyanate.Pyrolysis of the oximino-isoxazolinones (507 R=Me or Ph) gave fulminic acid, HCNO, which was trapped at -196... 

Thermolysis of (55) yields 1,2X, -azaphosphete (56), which undergoes reaction with boron trifluoride or methyl iodide with retention of the ring, while ring expansion reactions occur with isocyanates, isothiocyanates and acetylenedicarboxylates, and ring opening processes occur with water, carbon disulfide and penta-fluorobenzonitrile. An X-ray crystal structure is available for (56, R = NPr2 ) (94JA8087). 

Ring expansion of 1,3,2-diazaboracycloalkanes with phenyl isocyanate and isothiocyanate has resulted via insertion of two atoms of the double bond system into the ring. Similarly, three new heterocyclic organoboranes have been produced from heterocyclic aminoboranes and organic isocyanates. The synthesis and thermal rearrangement of boron carbamoylaminopyridin-ates of the type (30) and (31) have been discussed. ... 

The highly ring strained cyclopropanone (which is conveniently stored and used as a mixed ketal) also undergoes Schmidt chemistry to afford M-substituted jS-lactams along with ethyl carbamates in about a 1 1 ratio (Scheme 7.9). Presumably, the p-laclam is formed via the typical ring expansion mechanism described above. Ethyl carbamates are more mechanistically intriguing, requiring the formal loss of ethylene and N2 followed by recombination of a silylated isocyanate with ethanol. 

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