Chlorovinyl group

An example of this reaction in an acyclic case is given in equation 21. Dienyne 55 afforded compound 56 in a highly selective 1,4-addition. In this case the relative amount of the trans chloropalladation adduct was higher than in the reaction of 53 and the chlorovinyl group was 90% E54. 

P. Crews and E. Kho-Wiseman, J. Org. Chem., 1977, 42, 2812 formula (20) of this paper should have a chlorovinyl group instead of a 2-chloroethyl group. Plocamene B and plocamene D are reported here without comment, with absolute stereochemistry the same as violacene 2 (cf. refs. 297, 300). 

A special derivatization reaction is required for lewisite 1, which is so reactive that it cannot be determined by GC/MS in low quantities (e.g. below 10 ng per injection). It has been known for a long time that lewisite 1 reacts with compounds having an a, P-dithiol structure, such as 2,3-dimercaptopropanol-l (British-Anti-Lewisite (BAL) also used for medical treatment). The derivatization reaction can be performed at an analytical level and several examples have been described (29). The reaction product of lewisite 1 with 3,4-dimercaptotoluene, 2-(2-chlorovinyl)-5-methyl-l,3,2-benzodithiarsole (see (1)), is a useful derivative for GC/MS analysis. Its mass spectrum is simple with molecular ion peaks at m/z 290/292 and the base peak at m/z 229 due to the loss of the 2-chlorovinyl group (30). 

When studying metal atom exchange in the acetylene quasi-complexes formulated as metal chlorovinyls, Borisov and the author found that the chlorovinyl group retained its configuration during the reactions. Some of them, e.g.,... 

Bromo-2-chloro( 1 -octene-3-ones), 2889 (Z)-l-Bromo-l-chlorovinyl group, 980 Bromocresol (BC), 2884 Bromocryptine, 707 Bromodeoxyuridine, 1445 1 -Bromo-2,3-dichloro( 1 -octene-3-ones), 2889 Bromo-4-hydroxybenzaldehyde (BH), 2884 Bromoindole (BRI), 32, 33, 1212 Bromophenol (BP), 2884, 2905... 

The drive to define the toxicity of CWAs during WWII led to an extensive programme of research in the UK and USA. From early studies" it was clear that the more rapid injury produced by L and the immediate sensory irritation removed the latency of response characteristic of SM injury. There is also systemic toxicity associated with exposure to L that is similar to that produced by arsenic. Some authors conclude that the arsenic content of L is responsible for its systemic toxicity, but others point out differences that indicate alternative mechanisms of toxicity are involved. It is tempting to speculate that the chlorovinyl group produces a different tissue distribution for L compared with arsenic and this may be responsible for the different toxicity profile, but no specific studies of the toxicokinetics of L have been carried out. 

The possibilily of obtaining (100) by the allqrlation of (359) with 1,3-dichlor0-2-butene has also been studied [449]. However, this route was abandoned, since the hydrolysis of the chlorovinyl grouping of the product obtained (375) was accompanied by its decomposition. The diketone (100), containing one asymmetric center, as resolved into its optical isomers by enzymatic reduction with Curviilaria falcata and other microorganisms [114, 116]. 

To synthesize isomeric 3-substituted isoxazoles (301) the reaction of ethylene acetals of )3-ketoaldehydes (300) (readily available from -chlorovinyl ketones (57IZV949)) with hydroxylamine was employed. Owing to the comparative stability of the dioxolane group, this reaction gave exclusively 3-substituted isoxazoles (301) (60ZOB954). The use of noncy-clic, alkyl S-ketoacetals in this reaction resulted in a mixture of 3- and 5-substituted isoxazoles (55AG395). 

Treatment of cyclic vinylaziridine 105 with organocuprates of the R2CuLi type proceeds in a highly syn-selective manner (Scheme 2.29) [46], The syn stereochemistry of the reaction reflects the effect of the acetonide group, which directs the nucleophilic attack to the less hindered a-face. The formation of SN2 products 109 from the cyclic (chlorovinyl)aziridine 107 can be explained by assuming a syn-SN2 ... 

Several vinylidene complexes of the group VI metals have been obtained by heating n-chlorovinyl derivatives with tertiary phosphines, phosphites, arsines, or stibines (9, 30) ... 

It is predicted that in an acidic medium a protonated amino group will leave preferentially to many other groups. While this geminate element effect has not been investigated in such media, it is known that the salts of /3-alkylammoniumvinyl ketones are better ketovinylation reagents than /3-chlorovinyl ketones (Nesmeyanov and Rybinskaya, 1957). 

The place of an acetylene in these reactions may be taken by an olefin substituted by a group capable of elimination during the reaction. Thus, aliphatic diazo compounds and vinyl halides give pyrazoles,473 whereas diazomethahe and /J-chlorovinyl ketones give... 

In many of these applications, the ethynyl group is present in the starting material only in latent form, e.g. as a chlorovinyl substituent, from which it is liberated during the pyrolysis step. That even non-terminal acetylenes can be employed in these cycloaromatizations is illustrated by the protected cross-conjugated diacetylene 43 in Scheme 11. When this was subjected to hydropyrolysis at 900 °C, the diacetylene 44 was generated in situ and double-cyclized to corannulene (40) immediately [23]. 

All four proposals agree with the second-order kinetics usually observed. Mechanism (3) cannot be valid because it requires that the same stereoisomer be formed, whatever the nature of the initial isomer, whereas cis and trans isomers were shown experimentally to give the different products. Mechanism (4) was refuted by the fact that chlorovinyl ketones, PhC(0)C(CH3)=CHX, which cannot lose HX, undergo nucleophilic substitution of the group X in precisely the same manner as do the ketones... 

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