Dihalocarbene addition

Ihe A -benzoyl ester 117 undergoes dihalocarbene addition to yield the cycloadduct 118 <96JCS(P1)2553>. Attempted ring-expansions of 118 were unsuccessful. 

The cocatalytic effects of pinacol in the phase transfer catalysis (PTC) of dihalocarbene additions to alkenes were noted by Dehmlow and co-workers who showed that pinacol accelerates the PTC deprotonation of substrates up to pKa 27.7 Dehmlow also studied the effects of various crown ethers as phase transfer catalysts in the addition of dibromocarbene to allylic bromides.8 In Dehmlow s study, elevated temperature (40°C) and dibenzo-18-crown-6 did not give the highest ratio of addition/substitution to allyl bromide. However, the submitters use of pinacol,... 

Predictably, with enynes dihalocarbene addition occurs preferentially with the double bond (equation 17).63 64 The reaction of dichlorocarbene with allenes usually gives rise to spiro-linked dichlorocyclopro-panes (equation 18),65 but rearranged products are obtained in some cases (equation 19).65 66 Somewhat surprisingly, a measure of stereoselectivity has been observed in the formation of dichlorocyclopro-pylcarbinols from secondary allylic alcohols and dichlorocarbene (equation 20).67... 

TV-Benzoyl esters 372 and 374 undergo dihalocarbene addition with phenyl (tribromomethyl)mercury 371 to yield adducts 373 and 375, respectively [381] (Scheme 3.121). But A-methyl- and A-benzyl-substituted analogues of 372 and... 

The tri- and tetrahalides are in many cases readily available by dihalocarbene addition to the corresponding halo- or dihalo-alkene in other cases they may be obtained on a synthetically useful scale from carboxylic acids118 ... 

Botta, M., De Angelis, F., Gambacorta, A. The reaction between 2,3-dialkylindoles and dihalocarbenes. Additional evidence for the interconversion of the reaction intermediates. Gazz. Chim. Ital. 1983, 113, 129-132. 

Monoaddition of carbenes or carbenoids to allenes (Route d) has also been achieved, but addition of two carbenes to give spiropentane derivatives is difficult to avoid. Examples of successful applications of this approach are dihalocarbene additions to substituted allenes123) (Eq. 62) to give dihalomethylenecyclopropanes in good yields. 

More generally, cycloproparenes are available via dihalocarbene addition to cyclohexa-1,4-diene or synthetic equivalents, followed by base-induced twofold dehydrochlorination and aromatization. When the dichlorocarbene adduct of cyclohexa-1,4-diene, 7,7-dichlorobicyclo-[4.1.0]hept-.3-ene (3), was reacted with potassium /ert-butoxide in dimethyl sulfoxide a twofold elimination of hydrogen chloride occurred which was accompanied by migration of the resulting double bonds into the cyclohexene ring to give benzocyclopropene. This sequence, sometimes named Billups synthesis, provides the most convenient access to benzocyclopropene. ... 

Dihalocarbene addition to 24 is related to the addition of carbenes to CgQ, Buckminsterfullerene, which occurs across a Cg-Cg junction to give methanofullerenes, in preference to addition across the fullerene Cg-Cj junction. [58] 2-Adamantanylidene,[58] PhCCl, [58] and CCI2, [59] also behave in this manner. Interestingly, nucleophilic (MeO)2C also attacks a fullerene Cg-Cg junction. [60] Fullerene is a strongly electrophilic substrate, [61] and does not differentiate electrophilic (CCI2) from nucleophilic carbenes on the basis of the regiochemistry of their additions. 

A novel observation of participation in a carbene reaction serves as our final example here. enrfo-5-Hydroxymethyl-2-norbornene (238), which Factor and Traylor found to add mercuric ion with participation, affords oxohomobrendene derivatives (239) under dihalocarbene addition conditions. The process can be envisioned to proceed as shown in Eq. (71). 

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