Allyl urethanes

Functionalization of the double bond of 2-azabicyclo[2.2.2]oct-5-ene derivatives has been shown to be remarkably regjoselective. Thus, oxymercuration [112] and selenohalogenation [113] lead to adducts which are convenient precursors of iso-quinuclidin-5-one and -6-one, respectively. This means an excellent control of the polarity at the double bond termini by the nitrogen atom (Note that simple allylic urethanes also undergo regioselective oxymercuration). 

Pd(0)/phosphine complexes, or their precursors, in the presence of a suitable co-base, have also been shown to promote, in good yields (66-100%), the formation of allylic carbamates from various primary and secondary aliphatic amines, pressurized C02 and allylic chlorides, in THF, at ambient temperature [87a]. The choice of the added co-base (Base), used for generating the carbamate salt RR NC02 (BaseH)+, was found to be critical for high yields of O-allylic urethanes. The use of a guanidine (CyTMG) or amidine (DBU) base was optimal for this system (see also Section 6.3.1). ft is assumed that this chemistry passes catalytically through a mechanism similar to that illustrated in Scheme 6.19. This involves nucleophilic attack by carbamate anion on a (tt-allyl) palladium species, formed by the oxidative addition of the allylic chloride to a palladium(O) intermediate. 

The stereo- and regioselective cyclizations of the allylic urethanes (199) to oxazolidin-2-ones and/or perhydropyrroIo[l,2-c][l,3]oxazin-l-ones by iodonium and bromonium dicollidine perchlorates in dichloromethane via intermediate 203 have been studied. In this same manner, 204 was generated from 200. In the cyclization of 201 in the presence of bromonium dicollidine perchlorate, the only product recovered was 205, while a similar reaction with isomer 202 resulted in a mixture of 206 and 207(1 5 ratio, respectively) (83JA654). 

G-Allylic urethanes and carbonates are afforded from amines/alcohols, carbon dioxide and allylic chlorides by palladium catalysed reaction in the presence of an organobase. The choice of added base in the generation of carbamates/carbonates was critical for high yields... 

The thiol-ene type of cure is based on free-radical additions of thiols to unsaturated compounds. The unsaturated compounds are often, though not necessarily, allylic ftmctionalized resins, such as allyl ethers and allylic urethanes and ureas. The thiol-ene systems find application in poly(vinyl chloride) based flooring and in gaskets. 

Typical procedures. Allyl carbamate. [408] Ammonia was passed into a solution of allyl chlorofoimate (368 g, 3 mol) in benzene (1000 mL) at 25-35 °C until the reaction was complete. The ammonium chloride produced was filtered off and the salt was washed with small quantities of benzene. Distillation of the benzene solution through a short column gave 255 g (85% yield) of allyl carbamate allyl urethane), bp 73-75 °C at 2 mmHg. 

Unsaturated sulfonamides are recovered unchanged at temperatures normally required for ring closure and decompose at temperatures above 300 °C [669]. Allyl ureas decompose to give a large number of products [671]. Allyl urethanes react with hydrogenolysis of the C-N bond to form carbamates and a number of other products [671]. 

In contrast to the above additions A-allyl- and substituted A-allyl-amides, -urethanes, -ureas and -thioureas undergo intramolecular cyclization only in 6(3-96% sulfuric acid to give the corresponding oxazolinium and thiazolinium salts. Treatment of these cations with base yields 2-oxazolines and 2-thiazolines in moderate to good yields. The reaction is illustrated by the conversion of A-2-phenylallylacetamide (342) into 2,5-dimethyl-5-phenyl-2-oxazoline (343) in 70% yield 70JOC3768) (see also Chapter 4.19). 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

A similar approach was used by the Alcaide group [183] in the synthesis of tricyclic (3-lactams 6/1-391 from 6/1-390 (Scheme 6/1.99). In this domino process the primarily obtained it-allyl-Pd-complex reacts with the N-nucleophile of the urethane moiety to form a C-N-bond and a vinyl halide. The final step is then an intramolecular Heck-type reaction of the vinyl halide with the alkyne moiety and re-... 

Several examples of transition metal catalysis for the synthesis of piperidines appeared this year. Palladium catalyzed intramolecular urethane cyclization onto an unactivated allylic alcohol was described as the key step in the stereoselective synthesis of the azasugar 1-deoxymannojirimycin . A new synthetic entry into the 2-azabicyclo[3.3.1]nonane framework was accomplished through a palladium mediated intramolecular coupling of amine tethered vinyl halides and ketone enolates in moderate yields . A palladium catalyzed decarboxylative carbonylation of 5-vinyl... 

The principal kinds of thermoplastic resins include (1) acrylonitrile-butadiene-styrene (ABS) resins (2) acetals (3) acrylics (4) cellulosics (5) chlorinated polyelliers (6) fluorocarbons, sucli as polytelra-fluorclliy lene (TFE), polychlorotrifluoroethylene (CTFE), and fluorinated ethylene propylene (FEP) (7) nylons (polyamides) (8) polycarbonates (9) poly elliylenes (including copolymers) (10) polypropylene (including copolymers) ( ll) polystyrenes and (12) vinyls (polyvinyl chloride). The principal kinds of thermosetting resins include (1) alkyds (2) allylics (3) die aminos (melamine and urea) (4) epoxies (5) phenolics (6) polyesters (7) silicones and (8) urethanes,... 

Fortunately, a wide variety of functionality is compatible with the Ti-tartrate catalyst (see Table 6 A. 1), but the judicious placement of functional groups relative to the allylic alcohol can lead to further desirable reactions following epoxidation. For example, in 40, asymmetric epoxidation of the allylic alcohol is followed by intramolecular cyclization under the reaction conditions to give the tetrahydrofuran 41 [67]. Likewise, in the epoxidation of 42, cyclization of the intermediate epoxy alcohol occurs under the reaction conditions and leads to the cyclic urethane 43 [68]. 

The main oligoester chain of these compounds may also include fragments of urethanes, sul-foesters, amides, and others. Along with the end-acryl groups, they may contain other reactive groups, such as carboxylic, allyl, hydroxy lie, etc. 

Figure 14 Changes in the glossiness and color difference of etherified Sugi surfaces during UV irradiation. O, Cyanoethylated wood A, allylated wood , benzylated wood , untreated wood A, acrylic urethane resin-coated wood , acrylic silicon resin-coated wood. Note UV lamps were high-pressure mercury lamps with 80 W/ cm. Coatings were transparent. (From Ref. 30.)...

Intramolecular ureidoselenenylotion.1 Intramolecular cyclization of unsaturated urethanes with 1 followed by allylative deselenenylation results in net ureidoallylation. 

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