Heterocumulenes cycloaddition reactions

Ulrich, H. (ed.) 1967, Cycloaddition Reactions of Heterocumulenes, Academic Press New York - London... 

Due to the presence of a heterocumulene unit, sulphines may be considered as a group of compounds which are able to undergo cycloaddition reactions. Reaction of sulphines with enamines and phosphorus ylides reported by Sheppard217 and Trippett218 and their coworkers may be considered formally as an example of [2 + 2] cycloaddition. In fact, Sheppard and Dickman217 obtained a 1 1 adduct from thiofluorenone S-oxide and 1-morpholinocyclohexene to which they assigned the dipolar sulphoxide structure 168. 

Several unusual cycloaddition reactions of 9 with unsaturated ketones should be mentioned in conclusion the heterocumulene generated photolytically from 7 undergoes [8 + 2]-cycloaddition with tropone to form 33 (40%) the structure of the product has been unequivocally established by X-ray structure analysis 22,23). Once again, the affinity of phosphorus for oxygen is manifested an entirely analogous cycloaddition reaction is known for diphenylketene 26). 

Thermal [2+3] cycloaddition reactions of 4jt-electron component 3-benzylidene-5-phenyl-3/7-l,2-dithiole 189 with 2Jt-electron component heterocumulenes 190 provided a novel route to 2-(substituted amino)-trithiapentalenes 191a and 2-(substituted amino)-dithia-l-selenapentalenes 191b (see Equation 49 and Table 26) <1997HAG233>. 

A full account of the preparation and 1,3-dipolar cycloaddition reactions of this class of meso-ionic heterocycle (105) has now been published. Using olefinic dipolarophiles or heterocumulenes, a number... 

The palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes 530 with aryl isocyanates or diaryl-carbodiimides led to 4-vinyl-l,3-oxazin-2-ones 531 or l,3-oxazin-2-imines 532, respectively (Scheme 101). In the absence of phosphine ligands (PPhs, bis(diphenylphosphino)ethane (DPPE), l,3-bis(diphenylphosphino)propane (dppp), no conversion of heterocumulenes was observed. Starting from fused-bicyclic vinyloxetanes, both types of cycloadditions proceeded in a highly stereoselective fashion, affording only the r-isomers of alicycle-condensed 1,3-oxazine derivatives <1999JOC4152>. 

B-67MI51500 H. Ulrich Cycloaddition Reactions of Heterocumulenes , Academic Press, New... 

For reviews of cycloadditions of ketenes, see Ghosez O Donnell. Ref. 926 Brady Synthesis 1971, 415-422 Luknitskii Vovsi Russ. Chem. Rev. 1969,38, 487-494 Ulrich Cycloaddition Reactions of Heterocumulenes, Academic Press New York, 1967, pp. 38-121 Holder /. Chem. Educ. 1976, 53, 81-85. For a review of intramolecular cycload-dilions of ketenes to alkenes, see Snider Chem. Rev. 1988, 88, 793-811. 

Cycloaddition reactions of Heterocumulenes , H. Ulrich, Academic Press, New York, 1967. Neues iiber 1,3-Cycloadditionen R. Huisgen, Helv. Chim. Acta, 1967, 50, 2421-2439. 

Four-membered heterocycles are easily formed via [2+2] cycloaddition reac tions [63] These cycloaddition reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, p lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118 The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, l,4-benzoxazm-2-ones, l,2,4-tnazin-5-ones, and l,2,4-tnazm-3,5-diones accelerates [2+2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidme derivatives Starting from olefins, fluonnated oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-1,2-azaphospholes with fluonnated ketones leads to [2+2] cycloadducts [121] (equation 27)... 

Cycloaddition reactions of transient or isolable disilenes with heterocumulenes such as CX2 (X = S, Se) produce heterocyclic carbenes, for example, carbene 59, which has a disilane backbone. These carbenes are only transient species and were not isolated but were either trapped with C6o. or dimerization of the carbenes occurred to give the tetrathiafulvalene or tetraselenafulvalene analogues 28 <2002CEJ2730, 2005AGE7567>. 

The [2+2] cycloaddition of the Si=Si double bond of disilenes across a hetero double bond belongs to the most typical reactions for the preparation of disiletanes. Reaction of the supersilyl stabilized disilene 90 with PhHC=0 and Ph2C=S gave oxa- and thiadisiletanes 91 and 92, respectively (Scheme 15). The use of heterocumulenes 0=C=0 and 0=C=S in a similar cycloaddition reaction yielded oxa- and thiadisiletanes 44 and 31. The isolated disiletanes are colorless and oxygen, water, and thermostable compounds <2002CEJ2730>. 

The oxidation of fV-carbamoylimidazolidine-2-thiones (281) has been used to prepare 2,3,5,6-tetrahydroimidazo[l,2-cf][l,2,4]thiadiazol-3-ones (282) which undergo cycloaddition reactions with heterocumulenes to give a variety of heteropentalenes (81T2485). 

Cycloaddition Reactions Across C=N Bonds. Cycloaddition reactions of heterocumulenes are well known reactions. Like many of the other heterocumulenes carbodiimides form cyclodimers and cyclotrimers (see Section 2.4.1). The obtained dimeric... 

Carbodiimides also play a role as building blocks of numerous N-heterocycles. Examples are the cycloaddition reactions of carbodiimides. In the formation of [2-1-2] cycloadducts N-methyl-N -t-butylcarbodiimide is used as a marker to determine the mode of addition of isocyanates or isothiocyanates to carbodiimides. In these reactions addition across the C=N or the C=0 bond of the isocyanate or across the C=N or the C==S bond of the isothiocyanate can occur. Addition to the N-methyl-N -t-butylcarbodiimide always proceeds across the N-methyl double bond. Also, theretroreaction of the [2-1-2] cycloaddition reaction of carbodiimides can afford a different set of heterocumulenes. ... 

H. Ulrich, Cycloaddition Reactions of Heterocumulenes , Acsidemic Press, New York, 1967. 

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