Aiyl-alkyl bonds

The reactivity of dichloro carbene towards acetylenic bonds was systematically investigated by Dehmlow19, 20 with respect to substitution of the acetylene, especially those containing additional C-C multiple bonds. It was shown that with aiyl alkyl acetylenes, e.g. 1-phenyl-butyne-l, often the normal cyclopropenone formation occurs only to a minor extent (to yield, e.g. 14), whilst the main reaction consists of an insertion of a second carbene moiety into the original acetylene-alkyl bond (giving, e.g. 15) ... 

The lUPAC name of an ester is derived from the name of the corresponding carboxylic acid. The alkyl or aiyl group bonded to oxygen is named first, followed by the name of the acid in which the suffix -ic acid is replaced by the suffix -ate. 

Unlike elimination and nucleophilic substitution reactions foimation of oigano lithium compounds does not require that the halogen be bonded to sp hybndized carbon Compounds such as vinyl halides and aiyl halides m which the halogen is bonded to sp hybndized carbon react m the same way as alkyl halides but at somewhat slowei rates... 

The value of alkyl halides as stalling materials for the prepaiation of a vaiiety of organic functional gioups has been stressed many times. In our eailier discussions, we noted that aryl halides aie nonnally much less reactive than alkyl halides in reactions that involve caibon-halogen bond cleavage. In the present chapter you will see that aiyl halides can exhibit theii own patterns of chemical reactivity, and that these reactions aie novel, useful, and mechanistically interesting. 

Section 23.4 Aiyl halides aie less reactive than alkyl halides in reactions in which C—X bond breaking is rate-detennining, especially in nucleophilic substitution reactions. 

Alkyl aiyl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl-ojqrgen bond. The reaction yields phenol and alkyl halide. 

The palladium-catalysed cross-coupling of aryl halides or vinyl halides with dialkyl phosphonates (31) to yield dialkyl arylphosphonates and dialkyl vinylphosphonates, respectively, was first reported by Hirao and co-workers 69 the halides used most frequently are bromides and the reaction is stereospecific with haloalkenes. Subsequently, analogous reactions of alkyl alkylphosphinates (32), alkyl arylphosphinates (32), alkyl phosphinates (33), and secondary phosphine oxides (34), replacing [P—H] bonds with [P—C] bonds to yield various phosphinates and tertiary phosphine oxides, have been developed (Figure 7.1). Alkyl phosphinates (33) may be mono- or diarylated as desired by the selection of appropriate conditions. Aiyl and vinyl triflates have also found limited... 

This chapter concentrates on those processes in which oxidative cleavage of a carbon-silicon bond results in pr uction of the alkyl/aiyl fragment as an alcdiol henol. Other cleavage processes are dealt with, but more briefly. 

LTAl oxidizes diaiyl telhirides to diaiylteUurium diacetates. whUe the treatment of diaryl, divinyl, alkyl aiyl and dialkyl tellurides widi Pd(OAc)2 or Li2PdQ4 results in a new carbon-carbon bond bang formed (equations 48 and 49). 

The electrochemistry of Ge and Si porphyrins with o-bonded alkyl and aiyl groups has been investigated by Kadish and Guilard The reactions are complicated and must be carried out both in the dark and in the strict absence of O2. An insertion of O2 into the Ge-carbon bond of Ge(Por)(R)2 has been postulated but later studies show that these reactions are actually more complicated than initially suggested The reduction of Ge(Por)(R)2 and Si(Por)(R)2 occurs in either one or two single electron transfer steps. E1/2 values of —1.45 V and —1.48 V are obtained for the first reduction of Ge(OEP)(CH3)2 and Si(OEP)(CH3)2 in PhCN and no second reduction is observed in this solvent In contrast, Ge(TPP)(CeHs)2 is reduced in two steps which occur at - 1.10 and - 1.65 V in PhCN. Similar values of - 1.17 V and -1.72 vs. SCE are measured for the reduction of Ge(TPP)(CH2CsH5)2. First and second reduction poten-... 

The main theme of this chapter is the cleavage of alkyl-, aiyl- and vinyl-carboxyl single bonds by means of the fragmentation (decarboxylation) of carboxyl radicals (equation 1). The fragmentation of... 

Catalytic enantioselective allylic substitutions of aiyl- and alkyl- substituted phosphates (63) with commercially available allenylboronic acid pinacol ester (64) resulted in the formation of tertiary or quaternary C-C bonds. Reactions were promoted by sulfonate-bearing chiral bidentate Af-heterocyclic carbene (NHC) complexes of copper (66), which exhibited the unique ability to furnish chiral products arising from the Sj.,2 mode of addition. Allenyl-containing products (65) were generated in up to 95% yield, >98% 8 2 selectivity and 99 1 enantiomeric ratio (Scheme 21). ... 

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