Acylation Organotin reagents

Various organotin reagents react with acyl and aroyl halides under mild conditions without decarbonylation to give carbonyl compounds[390,39l]. Alkyl- or alkenyltin reagents react with acyl and aroyl chlorides to give ketones[548.733,734]. One example is the preparation of the a,/3-dnsaturated 7-keto esters 860 and 861, carried out under a CO atmosphere[735]. The reaction has been applied intramolecularly to the synthesis of the macrocyclic keto... 

Organomanganese(II) iodides, 210 Organotin reagents, 211 Organovanadium reagents, 219 From carboxylic acids Benzylchlorobis(triphenylphos-phine)palladium(II), 30 From other acyl derivatives Lithium o-lithiophenoxide, 166 Organomanganese(II) iodides, 210 From 1,2-diols or 1,2-amino alcohols Diethoxy triphenylphosphorane, 109... 

Coupling o( organotin reagents (and Pd catalyst) with atyl or vinyl halides or triflates, acyl chlorides or iMyl acetates. 

The use of organotin reagents (O Sect. 2.1.2 under O Formation of Organotin Intermediates ) provides a useful means of efficient regioselective acylations. There does not seem to be significant differences in selectivities between alkylation and acylation although forma-... 

On the other hand, since no migration resnlted with whether acetic anhydride or benzoyl chloride at room temperature, it is apparent that the results controlled by acyl reagents, where the 3,6-position protected product 37 was obtained with acetic anhydride whereas the 2,6-position protected product 38 was obtained with benzoyl chloride at room temperature, were not brought about by the organotin acyl group migration mentioned above (Scheme 9). 

An extension of this tin chemistry to the regioselective acylation of unprotected sugars bound to a resin shows the possibility of using solid-phase techniques for the preparation of 0-acyl derivatives of carbohydrates [231]. Very recently, it has been reported that organotin-mediated multiple carbohydrate esterifications can be controlled by the acylating reagent and the solvent polarity. When acetyl chloride is used, the reactions are under thermodynamic control, whereas when acetic anhydride is employed, kinetic control takes place (O Scheme 31) [232]. 

Prior to the studies which uncovered the utility of organotin acylation as described in the preceding paragraphs, acid chlorides were also found to undergo a similar rhodium(I)-mediated acylation with allyltins to form p, y-unsaturated ketones. The palladium(0)-catalyzed coupling has been found to be more general with respect to varied substitution patterns of both reagents and could be conducted under essentially neutral conditions (see Section 1.13.5.1). 

The acylation of organocadmium reagents with acid chlorides such as (115) formed an early method for synthesis of progesterone derivatives such as 21-methyl progesterone (equation 97). The same transformation may be accomplished more easily with palladium-catalyzed organotin acylation in 45%... 

Treatment of tributyltin hydride with a Grignard reagent enables preparation of the corresponding organotin anion, which undergoes the Cannizarro reaction with pentanal providing an acyl stannane (Scheme 12.130) [233]. 

A remarkable application of the stannylation procedure is the organotin-mediated monoacylation of diols with reversed chemoselectivity, by which monoesterification of unsymmet-rically substituted diols at the most substituted hydroxyl group can be achieved with acyl chlorides [60], In the reported mechanism [61], this unusual reversal of chemoselectivity rests on a fast intramolecular transesterification equilibrium in which the dibutylstannylene acetal plays the double role of reagent and catalyst. The knowledge of the reaction mechanism allows for adjustment of experimental conditions to achieve remarkable selective level which can be higher than 99% using appropriate reagents (Scheme 4). 

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