Carbamates from hydroxy compounds

Table 6. 4-Hydroxy-l-alkenyl Diisopropylcarbamates from 2-Alkenyl Carbamates and Carbonyl Compounds...

The A-(l-acyloxyalkyl)amides or carbamates arc easily prepared from the corresponding hydroxy compounds by conventional acylation methods, such as heating with the required carboxylic acid in the presence of a strong acid or treatment with acyl halides or acid anhydrides1. 

Benzo[6]thienyl N-methylcarbamate (tradename Mobam), and a number of other benzo[6]thienyl carbamates possessing insecticidal activity, have been prepared from the corresponding hydroxy compounds by means of standard reactions.610,6,1 Compounds 240 (X = 0,... 

Acetyluracil — Ethyl 2-hydroxy-4-methyl-5-pyrimidinecarboxylate (XXXVI), which is prepared by the cyclization of the ureidomethylene derivative of aceto-acetic ester, can be caused to rearrange into 5-acetyluracil (XXXVII) in dilute alkali [304]. Compound (XXXVII) can also be prepared from diketene and ethyl carbamate, followed by treatment with ethyl orthoformate and cyclization with ammonia [305]. 

The y-amino-p-hydroxy acid derived oxazolidinones 55 are prepared from the corresponding N-unprotected y-amino-p-hydroxy ester derivatives by reaction with phosgene,1119,391 carbonyl diimidazole,[41] or benzyl chloroformate.[86] Alternatively, cyclization is obtained from the N-carbamate protected derivatives, i.e. from the TV-isopropenyloxycarbonyl derivatives under heating,[381 or from the TV-Boc or N-Z derivatives under basic conditions. [68 81 87] By analogy, the p,y-diamino acid analogue is converted into the imidazolidinone 57 by treatment of the unprotected compound with phosgene.[83 88]... 

Carbamate esters also produced 2-oxo compounds, e.g., the esters of 3-aminopropanol88 and of 3-halogenopropanol.87 A few compounds have thus been prepared from carbamates, e.g., 20, with an aromatic substituent88 [Eq. (10)] or a heterocyclic one.89 Ethyl 7V-(3-hydroxy-propyl) urethanes cyclize to 2-oxo compounds with sodium methoxide.78 An interesting novel approach was to react an A-(chloromethyl)-carbamate with olefins to yield 2190 [Eq. (11)]. 

The activity of the ethanolic extract of both the pods and the seeds of M. oleifera is equivalent at the dose of 30 mg/kg. The ethyl acetate phase of the ethanolic extract of pods has more hypotensive potency at the same dose. The bioassay-directed fractionation ethyl acetate phase of the ethanohc extract of pods led to the isolation of thiocaibamate and isothiocyanate glycosides which are also the hypotensive compounds observed in M. oleifera leaves. Two new compounds, 0-[2 -hydroxy-3 -(2 heptei5rloxy)]-propyl undecanoate and O-ethyl-4-[(a-Z-rhamnosyloxy)-benzyl] carbamate along with methyl p-hydroxybenzoate and p-sitosterol are also isolated from the pods. The latter two compounds and /7-hydroxybenzaldehyde shows promising hypotensive activity (89). 

Diisocyanates are an important class of chemicals of commercial interest, which are frequently used in the manufacture of indoor materials. such as adhesives, coatings, foams and rubbers (Ulrich, 1989). In some types of particle board, the diisocyanates have replaced formaldehyde. Isocyanates are characterized by the electrophilic -N=C=0 group, which can easily react with molecules containing hydroxy groups, such as water or alcohols. On hydrolysis with water, primary amines are formed, while a reaction with alcohols leads to carbamates (urethanes). Polyurethane (PUR) products are then obtained from a polyaddition of diisocyanate and diol components. Compounds commonly used in industrial surface technology are 4,4 -diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). The diisocyanate monomers are known as respiratory sensitizers and cause irritation of eyes, skin and mucous membrane. Therefore, polyisocyanates such as HDI-biuret and HDI-isocyanurate with a monomer content <0.5 % are used for industrial applications, and isocyanate monomers will not achieve high concentrations in ambient air. Nevertheless, it is desirable to measure even trace emissions from materials in private dwellings. 

Ajmaline (14) was chosen as a starting material because its total synthesis and absolute configuration were already established (14-16), and furthermore, the equilibrium isomer 17 from ajmaline chemically corresponds to the hypothetical intermediate 13. Ajmaline (14) was first converted into the hydrazone derivative by treatment with A,)V-dimethylhydrazine and a catalytic amount of sulfuric acid. After protection of the resulting secondary amine with methyl carbamate, the hydrazone was hydrolyzed with cop-per(II) chloride in aq. tetrahydrofuran (pH 7) to afford the aldehyde 19 in 75% yield. The hydroxy group in compound 19 was protected with the methoxyethoxymethyl (MEM) ether, and then bromine was selectively... 

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