Nucleophiles sulfone conjugate bases, carbon

Other nucleophilic carbon reagents, such as acetylide ions, and ions derived from ot-methylpyridines have also been used. A particularly useful nucleophile is the methylsulfinyl carbanion, CH3SOCH2-, ° the conjugate base of DMSO, since the p-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 624). The methylsulfonyl carbanion (CH3SO2CH2), the conjugate base of dimethyl sulfone, behaves similarly, ° " and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF will acylate l,3-dithianes ° (see 10-71) to give, after oxidative hydrolysis with NBS or NCS, a-keto aldehydes or... 

Benzo[ ]thiophene 1,1-dioxide 38 and its derivatives act as typical a, ft-unsaturated sulfones, and a variety of nucleophiles add to the carbon atom at the 3-position. Thus, amines and the conjugated bases of water, alcohols, thiophenol, and diethyl malonate all add to 38 to give the corresponding adducts 110 in excellent yields (Scheme 65) [189]. Even hydrogen bromide can add to 38. When 2-bromobenzo[b]thiophene 1,1-dioxide 111 was treated with piperidine and morpholine under appropriate conditions, excellent yields of adducts 112 were isolated without being accompanied by dehydrobromination (Scheme 66) [190]. 

The conjugate base of an alkyne is an alkyne anion (older literature refers to them as acetylides), and it is generated by reaction with a strong base and is a carbanion. It funetions as a nucleophile (a source of nucleophilic carbon) in Sn2 reactions with halides and sulfonate esters. Acetylides react with ketones, with aldehydes via nucleophilic acyl addition and with acid derivatives via nucleophilic acyl substitution. Acetylides are, therefore, important carbanion synthons for the creation of new carbon-carbon bonds. Some of the chemistry presented in this section will deal with the synthesis of alkynes and properly belongs in Chapter 2. It is presented here, however, to give some continuity to the discussion of acetylides. 

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