Reaction Of Dimethoxycarbene Research Articles

Reactions of Dimethoxycarbene with N‐Tosylated Imines

AbstractThe reactions of dimethoxycarbene (DMC; 2), which was generated in situ by thermal decomposition of 2,5‐dihydro‐2,2‐dimethoxy‐5,5‐dimethyl‐1,3,4‐oxadiazole (1), with N‐tosylated imines of xanthone and 2,3 : 6,7‐dibenzosuberenone, 3a and 3d, respectively, led to different adducts with rearranged skeletons. In the case of 3a, the 1 : 1 adduct 5 as well as the 2 : 1 adduct 6 were obtained (Scheme 2). The formation of both products can be explained by a migration of a MeO group of the DMC fragment in a zwitterionic intermediate. On the other hand, migration of a Me group of DMC is necessary for the formation of the two 1 : 1 adducts 13 and 14 of 2 and 3d (Scheme 5). The structures of all products have been established by X‐ray crystallography.

The First Reaction of Dimethoxycarbene with an Imine Moiety

AbstractThe nucleophilic dimethoxycarbene (DMC; 2) generated by thermal decomposition of 2,5‐dihydro‐1,3,4‐oxadiazole derivative 1 in boiling toluene reacts smoothly with N‐(9H‐fluoren‐9‐ylidene)‐4‐methylbenzenesulfonamide (7b) to yield carbonimidoate derivative 10. A multi‐step reaction pathway, initiated by the attack of DMC onto the CN bond and followed by the migration of the sulfonyl group (or via a sulfinate anion) is proposed to explain the formation of the final product. In contrast to the formal ketimine 7b, N‐benzylidene‐4‐methylbenzenesulfonamide (7a), a formal aldimine, does not react with DMC under comparable conditions.

New Entry into β‐Lactams via Reaction of Dimethoxycarbene with Isocyanates.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Reaction of Dimethoxycarbene—DMAD Zwitterion with 1,2‐Diones and Anhydrides: A Novel Synthesis of Highly Substituted Dihydrofurans and Spirodihydrofurans.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Reaction of Dimethoxycarbene−DMAD Zwitterion with 1,2-Diones and Anhydrides: A Novel Synthesis of Highly Substituted Dihydrofurans and Spirodihydrofurans

The zwitterion formed by the reaction of dimethoxycarbene and DMAD adds efficiently to one of the carbonyl groups of 1,2-dicarbonyl compounds and anhydrides to generate dihydrofurans and spirodihydrofurans in good yields. In many cases, the carbene inserts into the C-C bond of the dione to yield masked vicinal tricarbonyl systems.

Reactions of Dimethoxycarbene with Carbon—Sulfur Double Bonds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reactions of dimethoxycarbene with xanthates

Dimethoxycarbene (DMC), generated by thermolysis of 2,2-dimethoxy-5,5-dimethyl–Δ3-1,3,4-oxadiazoline at 110 °C, in benzene in a sealed tube, reacted with most xanthates by formal insertion of the carbene into the S=C‒SR single bond. The reaction course is probably attack of the carbene at carbon of the C= S function, concomitant with (or followed by) migration of the SR group. The products, all new, are mixed orthoesters (two methoxy and one SR at the same carbon), a functional group that has been reported for one case only. In the case where the R group was CO2Me, the reaction became complicated, probably from initial attack at the carbonyl group.

Reactions of dimethoxycarbene with thiocarbonyl compounds

A diverse sample of thiocarbonyl compounds were examined to determine what the ultimate stable products are of their reactions with dimethoxycarbene. Those ultimate products can be significantly different for an oxyphosphinyl dithioformate, methyl dithiobenzoate, O-methyl thiobenzoate, and dimethyl xanthate. Key words: dimethoxycarbene, thiocarbonyl compounds, 2,5-dihydro-2,2-dimethoxy-5,5-dimethyl-1,3,4-oxadiazole.

Relative reactivities of carbonyl and thiocarbonyl groups toward dimethoxycarbene: two new dimethoxythiiranes.

Reaction of dimethoxycarbene (DMC), generated by thermolysis of a 2,5-dihydro-1,3,4-oxadiazole, with 2,2,4,4-tetramethyl-3-thioxocyclobutanone afforded primarily 2,2-dimethoxy-3,3,5,5-tetramethyl-4-thioxocyclopentanone from ring expansion by overall insertion into the C-CO bond. 4,4-Dimethoxy-2,2,5,5-tetramethyl-3-thioxocyclopentanone, from overall insertion into a C-CS bond, was a minor product. Thus the carbene had reacted preferentially at the carbonyl group, rather than the thiocarbonyl group of the four-membered ring. However, the minor product reacted with DMC at the thiocarbonyl group to afford a dimethoxythiirane. A product from a corresponding reaction at the carbonyl group could not be found. A rationale for the apparent reversal of relative reactivities of the carbonyl and thiocarbonyl groups is offered, with supporting evidence.

ChemInform Abstract: Reaction of Dimethoxycarbene with Strained Cyclic Carbonyl Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of dimethoxycarbene with strained cyclic carbonyl compounds

A cyclopropanone, a cyclopropenone, cyclobutanones, a cyclobutane-1,3-dione, and a cyclobutene-1,2-dione reacted with dimethoxycarbene to afford acetals of the next larger ring by formal insertion of the carbene into a C—C bond α to the carbonyl group. When either of two saturated α-ring carbons could be involved in the process, the ring expansion was selective, affording primarily the product of apparent insertion into the more substituted ring bond. With 2,3-dimethoxycyclobutene-1,2-dione, insertion occurred between the carbonyl groups and with β-propiolactone it occurred at the lactone bond. β-Propiolactam, however, reacted by insertion of the carbene into the N—H bond.Key words: β-propiolactone, cyclobutanone, cyclobutananedione, cyclopropanone, dialkoxycarbene.

ChemInform Abstract: Reactions of Dimethoxycarbene with Cyclic Perchlorinated Olefins and Ketones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactions of Dimethoxycarbene with Cyclic Perchlorinated Olefins and Ketones

Reactions of dimethoxycarbene (2), a carbonyl group equivalent, with perchlorinated olefins and ketones were investigated. Thermolysis of 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (1) at 110 °C generated 2, which reacted with hexachlorocyclopentadiene (4), octachlorocycloheptatriene (12), octachlorobicyclo[3.2.0]hepta-3,6-diene (24), hexachlorotropone (28), hexachlorobicyclo[3.2.0]hepta-3,6-dien-2-one (32), and tetrachloro-1,4-benzoquinone (35). Reactions of 2 with perchlorinated olefins 4, 12, and 24 led to esters or, in the case of 12, to a ketene acetal. Their formation is rationalized in terms of Michael-like addition and displacement (SN2‘ or SN2‘ ‘, if concerted) of allylic chlorine atoms by 2, yielding ion pairs that either dechloromethylate to esters or dechlorinate to a ketene acetal. In contrast, the reactions of 2 with unsaturated perchloroketones 28, 32, and 35 led to ring contraction, ring expansion, and aromatization, respectively. The products from these reactions are consistent with...

Laser Flash Photolysis Studies of Oxygen and Sulfur Atom Transfer Reactions from Oxiranes and Thiiranes to Singlet Carbenes1

Laser flash photolysis (UV-LFP) studies of benzylchlorodiazirine (1a), phenylchlorodiazirine (1b), phenylmethoxydiazirine (1c), 2,2-dimethoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazoline (6a), 3,4-diaza-2,2-dimethoxy-1-oxa[4.3]spirooct-3-ene (6b), 5‘,5‘-dimethoxyspiro[adamantane]-2,2‘-[Δ3-1,3,4-oxadiazoline] (6c), and diazofluorene (DAF) in the presence of oxiranes and thiiranes are reported. These compounds, upon irradiation, afford benzylchlorocarbene (2a), phenylchlorocarbene (2b), methoxyphenylcarbene (2c), dimethylcarbene (8a), cyclobutylidene (8b), adamantylidene (8c), and fluorenylidene (FL), respectively. Absolute rate constants for the transfer of oxygen and sulfur atoms to these carbenes have been determined in both acetonitrile and cyclohexane solvents. These carbenes abstract oxygen and sulfur atoms with bimolecular rate constants ranging from 104 to 1010 M-1 s-1 at 22 °C. Ylides from attack of carbenes onto heteroatom donors were not observed for any of the heteroatom transfer reactions. It was found that the magnitudes of the rate constants for heteroatom transfer are dependent on the philicity of the carbene intermediate, and trends in the kinetic data suggest that oxygen and sulfur atom transfers occur by concerted mechanisms through ylide-like transition states. The reactions of dimethoxycarbene (14) with cyclohexene oxide and propylene sulfide have been studied by the thermolysis of 6a, in benzene, at 110 °C. It was found that dimethoxycarbene also abstracts oxygen and sulfur atoms, albeit in low yields. It is concluded that, for singlet carbenes, carbene electrophilicity is important in these heteroatom transfer processes.

(Alkylthio)- and (phenylthio)methoxycarbenes from oxadiazolines

Four 2-methoxy-5,5-dimethyl-Δ3-1,3,4-oxadiazolines bearing an alkylthio or arylthio group at C2 were prepared. The oxadiazolines undergo thermolysis at 60–80 °C in solution to afford the corresponding oxythiocarbene intermediates. In the absence of carbene traps, dimers of the carbenes were formed. The carbenes were trapped with ethyl crotonate, with dichloromaleic anhydride, with dimethyl acetylenedicarboxylate, and with phenyl isocyanate. Phenyl isocyanate traps methoxy(methylthio)carbene to form two types of adducts, both fundamentally different from the product obtained from reaction of dimethoxycarbene with phenyl isocyanate. All of the adducts have structures consistent with nucleophilic behaviour of the carbenes. Key words: oxythiocarbene, oxadiazoline, thermolysis, nucleophilic.

ChemInform Abstract: Reactions of Dimethoxycarbene and Fluoromethoxycarbene with Hydroxyl Compounds. Absolute Rate Constants and the Heat of Formation of Dimethoxycarbene.

AbstractFrom diazirine (II) the carbene precursor (IV) is obtained and the reactions of carbene (V) with alcohols (VI) and with AcOH are examined.

Reactions of dimethoxycarbene and fluoromethoxycarbene with hydroxyl compounds. Absolute rate constants and the heat of formation of dimethoxycarbene

Reactions of dimethoxycarbene and fluoromethoxycarbene with hydroxyl compounds. Absolute rate constants and the heat of formation of dimethoxycarbene