Carbenes alkoxy chloro

Flash pyrolysis of 4-arylmethylidene-3-methyl-5(4//)-isoxazolones (127) yields phenylacetylenes with alkoxy, chloro, dimethylamino and hydroxy substituents. The reaction proceeds via an arylmethylidene carbene as has been described for a... 

In 1986, Kesselmayer and Sheridan reported the matrix isolation and IR spectrum of chloro-methoxymethylene. They were able to show that two isomeric forms were present, trans (12) and cis (13). This is in line with Schaefer s " finding that hydroxymethylene should exist in cis- and frons-forms. While Kesselmayer and Sheridan were able to assign several of the bands in the matrix mixture to the cis- and trans-forms, they were unable to assign the majority of the bands in the IR spectrum they obtained to the specific isomer. In order to further confirm their isolation of these alkoxy carbenes, as well as to help in the interpretation of the observed IR spectrum, we undertook the calculation of the IR spectra of 12 and 13. ... 

Fu and co-workers have shown that the l-chloro-boracyclohexa-2,4-diene 97 reacts with 4-phenylpyridine at room temperature to provide the />-terphenyl analog 26 in 76% yield as an early example of a borabenzene-pyridine-type complex (Equation 6). The X-ray structure of 26, discussed in Section 7.14.3, shows the three rings not to be coplanar <1997OM1501>. Exposure of the l-chloro-boracyclohexa-2,4-diene 98 to a stabilized carbene results in formation of the complex 29 in 83% yield as an air- and moisture-sensitive colorless powder (Equation 7), crystals of which were grown from toluene the X-ray structure of 29 has been discussed in Section 7.14.3. The use of bulky lithium bases to deprotonate the bis(amido) or bis(alkoxy)boranes 19 allows for the formation of the dianionic 2,2 -diboratabiphenyl derivatives 20 (X = NHPh, OBn), the solid-state structures of which have been discussed (Equation 8) <2006CJC81>. 

Alkoxy(or -aryloxy)halocarbenes are ambiphilic (for selectivity indices, see ref 9), they react at a high rate with electron-rich and electron-poor alkenes, however, they react at a slow rate, with alkenes of intermediate reactivity. Steric hindrance decreases the rate addition of fluoro- and chloro(phenoxy)carbene to 2,3-dimethylbut-2-ene. ° For discussion of structure-activity relationship of carbenes, see ref 9, and Houben-Weyl, Vol. El9b, pp 14-34. 

Bis(organooxy)diazirines are available by exchange of chlorine in 3-alkoxy-3-chloro-3//-diazirines for the alkoxy group. The diazirines thus formed decompose under mild conditions, at room temperature, to generate the bis(organooxy)carbenes which undergo addition to electrophilic alkenes to give cyclopropanes... 

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