Allenes isocyanate

Ketenes easily add water,alcohols, amines and thiols to give derivatives of phosphorylated carboxylic acids ( -7). Phosphorylated ketenes undergo reactions of cyclo"aadition to vinyl ethers,diazomethane,styrene, cyclopentadiene, etc. From phosphorylated ketenes other phosphorylated cumulenes can be obtained,for example allenes,isocyanates,ketenimines... 

The number of monomers that undergo chain-growth polymerization is large and includes such compounds as alkenes, alkynes, allenes, isocyanates, and cyclic compounds such as lactones, lactams, ethers, and epoxides. We concentrate on the chain-growth polymerizations of ethylene and substituted ethylenes and show how these compounds can be polymerized by radical and organometallic-mediated mechanisms. 

Monomers used for chain-growth polymerization include alkenes, alkynes, allenes, isocyanates, and cyclic compounds such as lactones, lactams, ethers, and epoxides. 

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon 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, (1 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, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... 

The reactive compound chlorosulfonyl isocyanate (ClSOaNCO, forms P-lactams even with unactivated alkenes, as well as with imines, allenes, conjugated dienes, and cyclopropenes. With microwave irradiation, alkyl isocyanates also... 

The addition of isocyanates (isoelectronic to CO) to group 14 carbene analogs was investigated in order to see if the resulting molecules w ould have an allene-like framework. In the first study, Wcidenbruch et attempted to synthesize... 

Simple allenes can also react with chlorosulfonyl isocyanate (CSI) to afford a-alky-lidene-/l-lactams 8 and 2-carboxamido-l,3-butadienes 9 [8],... 

Allenes react with isocyanates to give the a-alkylidene-/Mactams. The highly reactive chlorosulfonyl isocyanate (CSI) is often used. Initial nucleophilic attack of the central allenic carbon atom to the central isocyano carbon atom produces an allylic cation intermediate, which cyclizes to the /i-lactam. 

Phenyl isocyanate reacted with highly reactive allenes 59 and 7 to give the corresponding [2 + 2]-cydoadducts [59]. 

The anodic oxidation of substituted allenes [76-79] and hetero-allenes [80-85] has been extensively studied by Becker and coworkers. Oxidation of secondary and tertiary alkyl isothiocyanates resulted in an ot-cleavage processes [77]. Primary alkyl isocyanates yielded amides and carbonyl compounds due to the nucleophilic involvement of either acetonitrile or water [80]. Primary alkyl isothiocyanates 48 afforded five-membered thiadiazolidine 49 and 50 and... 

P. Walden34 has studied soln. of iodine in acetaldehyde, hydrazine hydrate, and acetonitrile J. H. Mathews, soln. of iodine in pyridine, ethyl, allyl, and plienyl isothiocyanic esters, and phenyl isocyanate while H. A. Allen has studied soln. of bromine and iodine in various oils. 

An account has appeared166 of [3,3]-(and [2,3]-)sigmatropic rearrangements of propargyl precursors that lead to the synthesis of allenes bearing functional groups with at least two heteroatoms (see Scheme 36). The allyl cyanate to isocyanate rearrangement has been established as a new synthetic method for the construction... 

The 1,2-functionalization of the allene moiety in 2-azetidinone-tethered alleny-nol derivatives has also been explored [96]. Carbamate 174 was selected as the starting material for the palladium(II)-catalyzed reaction. The above carbamate was prepared from the ot-allenic alcohol 171a by treatment with tosyl isocyanate. Reaction of compound 174 was carried out at room temperature in acetonitrile in the presence of 10 mol% of Pd(OAc)2, 5 equiv of LiBr, 2 equiv of Cu(OAc)2 and 1.2 equiv of K2CO3 under an atmospheric pressure of oxygen. The 1H-XMR spectrum of the crude material displayed neither signal corresponding to the allene... 

Moricini and Kelly [75] have reported the synthesis of spiro-fi-lactams 6 containing an exocyclic double bond (Scheme 2) by the 1,2-dipolar cycloaddition of symmetrically/unsymmetrically substituted allene 4 with chlorosulfonyl isocyanate 5 in ether. 

Scheme 35 Regiochemistry of the reaction between allenes (139) and isocyanic acid...

The reaction between isocyanic acid and allenes was also studied and showed different regiochemistries depending on the substitution pattern (Scheme 35). Thus, in the simplest case (not studied experimentally), the formation of the 4-substituted cycloadduct (141) is predicted to be strongly favored, mainly because of the lower distortion of the allenic moiety at the transition structure (140). In contrast, substituted allenes such as 1,3-dimethylallene form the 3-alkylidene derivative (143) via a more stabilized transition structure like (142), in good agreement with the experimentally observed regiochemistry[113-115]. 

An ab initio study of the 2 + 2-cycloadditions of allene to isocyanic acid and ketene to vinylimine found the reactions to be concerted and mostly asynchronous.28,29 The diastereoselective 2 + 2-cycloaddition of dichloroketene with a chiral enol ether (26) produced the cyclobutanone (27), which leads to a key intermediate (28) in (g) the total synthesis of the natural alkaloid (-)-Swainsonine (29) (Scheme 8).30 The... 

Dobrowolski and co-workers reported calculations of the thermodynamic stability of the products derived from cycloaddition of vinylimine and ketene and of isocyanic acid and allene using MP2, density functional theory (DFT) (B3PW91), and Hartree-Fock (HF) methods with the 6-311+- -G basis set. Fourteen different structures were calculated for these cycloaddition reactions and the values of the free Gibbs energy showed that only 4- and 3-methylene-/3-lactams could be formed in considerable amount. 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

---