Methylcarbamates synthesis

Finally in 2005, Hutt and Mander reported their strategy for the synthesis of nominine (Scheme 1.3) [29], The approach relies upon construction of the steroidal ABC carbocyclic ring structure followed by stepwise preparation of the fused aza-ring system. In the key sequence of the synthetic study, enone 50 was oxidized to dienone 51 with DDQ followed by Lewis acid-catalyzed intramolecular conjugate addition of the methylcarbamate to the newly formed dienone to deliver pyrrolidine 52. 

Various nucleophiles other than methanol can be introduced onto the carbonyl carbon. Anodic oxidation of acylsilanes in the presence of allyl alcohol, 2-methyl-2-propanol, water, and methyl /V-methylcarbamate in dichlorometh-ane affords the corresponding esters, carboxylic acid, and amide derivatives (Scheme 24) [16]. Therefore, anodic oxidation provides a useful method for the synthesis of esters and amides under neutral conditions. 

Needless to say, it would be interesting to apply the same type of chemistry described in Figure 2 for the methylcarbamate esters to the synthesis of derivatives of the formamidine insecticides. However, additional work with the formamidines, particularly those related to chlordimeform, has been discouraged because of the mutagenic and carcinogenic potential of the aryla-mine metabolic products. 

More recently, an interesting reaction was discovered which provides the means for the synthesis of a wide variety of methylcarbamate derivatives containing the N-sulfinyl [N-S(O)] moiety (34). In attempting to prepare isopropoxy-N-methyliminoyl chloride by the reaction between Isopropyl methylcarbamate and thionyl chloride, an unexpected product, isopropyl ll-chloro-sulfinyl-N-methylcarbamate was obtained according to the equation below. The same product also was obtained when the... 

A general methodology for the construction of quaternary carbon atoms at the carbonyl carbon of ketones has been successfully exploited for the facile synthesis of ( )-lycoramine (299) (Scheme 30) (165). Thus, the O-allylated o-vanillin 322 was allowed to react with vinyl magnesium bromide followed by Jones oxidation, and the acid-catalyzed addition of benzyl IV-methylcarbamate to the intermediate a,(3-unsaturated ketone furnished 323. Wadsworth-Emmons olefination of 323 with the anion derived from diethyl[(benzylideneami-no)methyl]phosphonate (BAMP) provided the 2-azadiene 324. The subsequent regioselective addition of n-butyllithium to 324 delivered a metalloenamine that suffered alkylation with 2-(2-bromoethyl)-2-methyl-l,3-dioxolane to give, after acid-catalyzed hydrolysis of the imine and ketal moieties, the 8-keto aldehyde 325. Base-catalyzed cycloaldolization and dehydration of 325 then provided the 4,4-disubstituted cyclohexenone 326. The entire sequence of reactions involved in the conversion of 323 to 326 proceeded in very good overall yield and in one pot. 

Drabel, J., Bachmann, F. (1983) Proinsecticides structure-activity relationships in carbamoylsulfenyl N-methylcarbamates. In Synthesis and Structure-Activity Relationships. Doyle, P., Fujita, T., Eds., pp. 211-211, Pergamon Press, Oxford, England. Eadie, B.J., Robbins, J.A. (1987) 11. The role of particulate matter in the movement of contaminants in the Great Lakes. In Sources and Fates of Aquatic Pollutants. Hites, R.A., Eisenreich, S J., Editors, pp. 318-364, Advances Chemistry Series 216, American Chemical Society, Washington DC. 

Synthesis of 10/7-pyrrolo[l,2- ][l,2,5]benzothiadiazocine 5,5-dioxide was reported by intramolecular cyclization of l-(2-formylamidomethylphenylsulfonyl)-17/-pyrrole 80. Treatment of the key intermediate 79 with triphosgene affords 10/7-pyrrolo[l,2-A][l,2,5]benzothiadiazocine-12(lli7)-one 5,5-dioxide 39, which can be also prepared by cyclization of the corresponding methylcarbamate 81 (Scheme 17 <1995JHC1779>). 

Figure 4.8 Synthesis of substituted phenyl N-methylcarbamate insecticides.

In 1999 it was again Weinreb who used this chemistry in the context of the total synthesis of the marine sponge alkaloid agelastatin A (Scheme 59, see also Scheme 24) [70]. This time M-sulfinyl methylcarbamate 231 was used to yield cycloadduct 233 which was opened to allylic sulfoxide 234. Heating in HMPTA/EtOH delivered via [2,3]-a rearrangement a mixture of the desired cyclized carbamate 236 and the open-chain transesterification product 237, which also cyclized under the influence of base. 

Although the direct synthesis of DMC starting from urea and methanol would be very attractive, its thermodynamics is not favorable, the calculated AG° for the direct transesterification reaction being about 3kcal at 100°C. The reaction involves two steps first, urea is converted to methylcarbamate by reaction with methanol at relatively low temperatures (ca. 100°C in the presence of a catalyst or ca. 150°C without catalyst) then, the carbamate is further reacted with methanol at 180-190°C in the presence of a catalyst to produce DMC, according to the reactions (10a) and (10b). 

The success of carbaryl encouraged the synthesis of N-methylcarbamates of other aromatic phenols. The N-methylcarbamates of alkyl- and chloro-substituted... 

Synthesis Predictions. LHASA suggested that carbaryl could be synthesized by reaction of N-methylcarbamic acid witii either 1- or 2-chloronaphthalene in the presence of strong base. The literature reference that LHASA provided and associated with this route indicates that the reaction proceeds through a benzyne intermediate. LHASA failed to suggest the commercial route (68) that proceeds via... 

NFPA Health 4, Flammability 3, Reactivity 2 Uses Intermediate organic synthesis in mfg. of methylcarbamate pesticides such as carbaryl and aldicarb smaller quantities used in prod, of polyurethane foams, plastics, certain pharmaceuticals Regulatory HAP... 

Synthesis of 2-methoxy-4-propenylphenyl methylcarbamate, 11. Into a 500 ml one-necked round-bottomed flask, 10.0 g (0.0609 mole) of 9 (2-methoxy-4-propenylphenol) was dissolved in 200 ml of ligroin (b.p. 20-40 C). To this solution, 6.94 g (2 x 0.0609 mole) of methyl isocyanate and 200 pml of triethylamine were added. The mixture was stirred by a magnetic stirrer and heated by means of a heating mantle to the reflux temperature for 57 hours. 

The hydroxybenzo[6]thiophens have also been used for the synthesis of carbamates with insecticidal effects. One of them, 4-benzo[6]thienyl methylcarbamate, (mobam) (403), exhibited a favourable combination of... 

The same authors studied the synthesis of 2-alkoxy-5-n-propyl- or 2-alkoxy-5-sec-butylphenyl methylcarbamates as active intermediates for insecticides [218]. This involved phosgenation of the substituted phenol, followed by aminolysis of the formed chloroformate with monomethylamine. As already discussed, methylcarbamates can also be synthesized by reacting the appropriate phenol with methyl isocyanate. Thus, 2-isopropoxy-5-sec-butylphenyl chloroformate was synthesized by treating 2-isopropoxy-5-sec-butylphenol with phosgene. The product was reacted with monomethylamine to obtain the desired 2-isopropoxy-5-sec-butylphenyl methylcarbamate. Similarly, 2-sec-butoxy-5-sec-butylphenyl methylcarbamate, 2-iso-propoxy-5-n-propylphenyl methylcarbamate, and 2-sec-butoxy-5-n-propylphenyl methylcarbamate were also synthesized. 

Lambrech of Union Carbide Corporation was issued two patents (19-20) covering the synthesis of 1-naphthyl N-methylcarbamate, known by the tradename Sevin, and its use as a insecticide. In method 1, 1-naph-thol or its sodium salt reacted with phosgene to give 1-naphthyl chloroformate which when reacted with methylamine afforded Sevin in excellent yield. 

Other variants of this reaction involve the use of HCl salts of a volatile secondary amine in the presence of sodium acetate in DMF [434], dimethylammonium di-methylcarbamate [435] or catalysts [436]. Microwave irradiation leads to good yields of thioamide derivatives in short reaction times [437]. Transformations of dialdehydes with secondary diamines in the presence of sulfur can be used for the synthesis of polymers [438]. 

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