Phosgene dimer

The reactions of (5)-5-hydroxymethyl-2-pyrrolidinone (236) with phosgene or phosgene dimer (trichloromethylchloroformate) in the presence of pyridine afforded (+)-(S)-3,5-dioxo-perhydropyrrolo[l,2-c]oxazole (243) in moderate yield <92H(33)619>. In a similar manner, tri-substituted oxazolidinones have been obtained <84EUP128120>. 

Reportedly, simple alkyl isocyanates do not dimerize upon standing. They trimerize to isocyanurates under comparable reaction conditions (57). Aliphatic isocyanate dimers can, however, be synthesized via the phosgenation of A[,A[-disubstituted ureas to yield /V-(ch1orocarhony1)ch1oroformamidine iatermediates which are subsequendy converted by partial hydrolysis and base catalyzed cycUzation. This is also the method of choice for the synthesis of l-alkyl-3-aryl-l,3-diazetidiones (mixed dimers of aromatic and aUphatic isocyanates) (58). 

A, A /-Carbonylbis[2(3//)-benzoxazolethione], obtained from mercaptobenzoxazole and dimeric phosgene as the more thermodynamically stable A-acyl product, also represents a reactive heterocyclic diamide of carbonic acid, and is therefore used in the same way for ester syntheses as A /V -carbonyldibenzimidazole.c 1321... 

Heterocyclic coupling components that have been coupled with diazotized ami-nophenyltrimethylammonium chloride are l-alkyl-6-hydroxy-2-pyridone [93], 1-amino-3-hydroxy-isoquinoline [94], and 2,4-diamino-6-hydroxypyrimidine [95], The trialkylammoniumaryl residue may also be connected to the aromatic diazo component via a sulfone or a sulfonamido function [96], Disazo dyes in this series (e.g., 34) [77901-21-4] may also be generated from monoazo dyes that still contain a primary amino group by dimerization using phosgene [97] or cyanuric chloride [98],... 

Disazo dyes are obtained by using coupling components with a primary amino group and dimerization with phosgene [111]. The diazo components are prepared by exhaustive alkylation of amino methylated 2-aminonaphthalene-1 -sulfonic acid, followed by scission of the sulfonic acid group in the presence of mineral acids [112],... 

If methyleneindoline-o)-aldehydes are condensed with cyclic amines substituted by an amino group in the aromatic ring, dyes are obtained that can be dimerized either by reaction with cyanuric chloride in a molar ratio of 2 1 or with phosgene. On account of their high substantivity these dyes are suitable for dyeing bleached sulfite pulp [22],... 

A sterically hindered (2,4,6-tri-t-butylphenyl)[bis(trimethylsilyl)]phosphine (9), whose crystal structure has been reported84, was utilized to form a 1-phosphabuta-l,3-diene (equation 67)36. Mes -substituted phosphaketene was obtained from the reaction of 9 with phosgene (equation 68)4. Reaction of 9 with thiophosgene afforded dimeric phosphathioketene, [Mes P=C=S]2 (equation 69)85. A."V3-Dithioxophosphorane was also isolated by introduction of the bulky substituent (equation 70)86. 

In another example, surprisingly, we found that the phosgenation of a substituted isoxazolamine hydrochloride doesn t afford the expected free isocyanate but a peculiar dimer according to the mechanism depicted on scheme 126 (Ref. 179). 

Scheme 126 A peculiar isocyanate dimer from phosgenation of substituted isoxa-zolamines.

In this volume, we have already examined some alternatives to the synthesis in situ and/or to the use of methyl isocyanate. We thought that 1,3-dimethyl diazetidine dione (XII) (methyl isocyanate dimer) should be a suitable methyl isocyanate precursor which can release methyl isocyanate in safe conditions. This dimer was prepared from N-chlorocarbonyl-N-methyl N -methyl urea (XI) obtained by phosgenation of N,N -dimethyl urea as previously described in scheme 156, section 3-3-4. Cyclization of (XI) in a suitable solvent and in presence of a base such as DABCO afforded the expected dimer (XII) as depicted in scheme 220. 

Cr(CO)6 is resistant to oxidation by halogens, unlike its Mo and W analogues. No reaction occurs with Br2 or I2 at RT CI2 effects oxidation to CrCla and phosgene. On the other hand, substitution of the carbonyl ligands by weaker tr-acid donors, such as bipyridine, thio ethers, or arsines, leads to complexes that are more easily oxidized. In some cases, such as Cr(CO)4L (L2 = 2,2 -bipyridine or 2,5-dithiahexane ), spectro-photometric changes and loss of CO are consistent with oxidation by Br2 and I2, though no isolable complex was obtained. If L is bis(l,2-dimethylarsino)benzene (diars), oxidation to Cr(diars)X3 (X = Br, I) occurs these Cr(III) complexes are likely dimers . ... 

The above dimer could be carbonylated to the tetramer by further treatment with phosgene in the presence of triethylamine [177]. 

The reactions of Af-silyl-substituted ketimine derivatives with phosgene result in the formation of acyl isocyanates, which trimerize or dimerize under the reaction conditions [1854] ... 

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