Polyfunctional acylating

Interfacial polymerization between a piperazine, or an amine-substituted piperidine, or cyclohexane, and a polyfunctional acyl halide [46,47]. 

Katritzky AR, Widyan K, Kirichenko K (2007) Preparation of polyfunctional acyl azides. J Org Chem 72(15) 5802-5804... 

Compared to the chemical modification reactions of PS, alkylation and acylation reactions are preferred to other reactions, such as halogenation, nitrolation, sulfo-nation, amination, and chloromethylation, etc. because the obtained polyfunctional PS has higher physico-me-chanical properties. 

The acylation reaction of PS with organic anhydrides, such as maleic and acetic anhydrides, are very important for synthesizing polyfunctional (carbonyl-, carboxyl-, keto-, olefinic) PS. The incorporation of these groups to PS caused an increase of adhesion capability, physico-mechanical properties, elasticity, and photosensitivity [41-46]. 

Suitable chemistry must be chosen to allow the use of polyfunctional, unprotected reagents. In general, acylations and other reactions with electrophiles of a support-bound substrate will require the protection of functionalized side chains, both in the substrate and in the reagent. Protected, polyfunctional reagents are, however, rare and expensive, and protections/deprotections add further synthetic steps to the synthesis. Nucleophilic transformations, on the other hand, often enable the direct use of highly functionalized, unprotected reagents. Hence, nucleophilic transformations (e.g. 

Based on the very different behaviors of lipases A (CAL-A) and B (CAL-B) from Candida antarctica towards polyfunctional compounds in non-aqueous media, Liljeblad et al82 reported a novel lipase-catalyzed method for the resolution of A -heterocyclic amino esters using methyl pipecolinate 69 as a model compound. For this purpose, the chemo-and enantioselective alcoholysis and transesterification reaction of 69 in the presence of CAL-B and the A-acylations using CAL-A were studied, (cf. fig. 37 and 38). 

Functionalized chromium carbene complexes can be prepared by the reaction of polyfunctional diorganozincs with photochemically generated Cr(CO)5.THF. The resulting intermediate ate complexes furnish under 1 atm of carbon monoxide an acyl complex which can be treated with Meerwein salt (Me30+ BF4" in dry CH2C12) at -30°C to give a chromium carbene complex (Scheme 9.3). 

A flexible and convergent access to 2,3-disubstituted benzo[b]thiophenes has been developed (Scheme 22). The most concise approach involves a sequential coupling of an o-bromoiodobenzene with benzylthiol and zinc acetylides leading to the adduct 78. Treatment with iodine followed by an iodine/magnesium exchange and acylation provides the polyfunctional benzofuran derivatives. a... 

The method is said to be more reproducible than a direct vanillin acylation as uncontrolled losses of this volatile intermediate product are obviated. Esselman and Clagett [187] determined the position of the oxygen atom in the chain of polyfunctional fatty acids. The method is based on the reduction of keto, hydroperoxy, epoxy and carboxyl groups to the corresponding alcohols with LiAlH4, subsequent silylation with BSA and the analysis by GC—MS using OV-1 at 225°C. 

The potential of the reverse polarity approach has been spectacularly demonstrated in a plethora of synthetic studies. A representative example can be found in Seebach s preparation of the antibiotic vermiculin. The key step of this synthesis involved the preparation of a polyfunctional intermediate 253 via the sequence shown in Scheme 2.102. The first stage of this sequence couples the formyl anion equivalent 244 with bromoepoxide 254. The primary bromide is more active as an electrophile than epoxide and therefore, under carefully controlled conditions, the product 255 is formed selectively. Under somewhat more stringent conditions the epoxide ring present in the latter adduct reacts as an electrophile with the second acyl anion equivalent 256 to yield adduct 257. In this sequence, 254 was used as an equivalent to the 1,4-doubly charged synthon CH2CH2CH(OH)CH. In the final step of this scheme, carbanion 258 was generated and reacted with dimethylformamide to produce the required product 253. It is remarkable that all of these sequential operations are carried out in one reaction vessel without the isolation of any intermediate products. The overall yield of 253 is rather high (approximately 52%). 

A limitation in the use of pivaloyl esters as protecting groups in a polyfunctional system is the harsh condition required for its cleavage (especially at sterically hindered secondary centers). The 4-acetoxy-2,2-dimethylbutanoyl (ADMB) esters have been proposed as an alternative because they are easily prepared, show similar reactivity in carbohydrate acylations, and are removed under much milder conditions (catalytic quantity of DBU at room temperature) [254]. 

In dithioacetals the proton geminal to the sulfur atoms can be abstracted at low temperature with bases such as Bu"Li. Lithium ion complexing bases such as DABCO, HMPA and TMEDA enhance the process. The resulting anion is a masked acyl carbanion, which enables an assortment of synthetic sequences to be realized via reaction with electrophiles. Thus, a dithioacetal derived from an aldehyde can be further functionalized at the aldehyde carbon with an alkyl halide, followed by thioacetal cleavage to produce a ketone. Dithiane carbanions allow the assemblage of polyfunctional systems in ways complementary to traditional synthetic routes. For instance, the p-hydtoxy ketone systems, conventionally obtained by an aldol process, can now be constructed from different sets of carbon groups. ... 

In this chapter, only special examples of stoichiometric acylation will be commented. For example, reactions showing extraordinary level of regiose-lectivity promoted by proximity or metal template effects are described. Moreover, examples of efficient use of carboxylic acids and esters as acylating agents under soft experimental conditions in combination with ecocompatible solvents are stressed as new and practicable synthetic methods. Studies on the highly efficient multistep s)mthesis of polyfunctional compounds via bis-acylation and alkylation-acylation processes are commented upon, and some mechanistic details are also shown. 

Reduction of Acyl Derivatives to Aldehydes. Aroyl chlorides and bromides give modest yields of aryl aldehydes when refluxed in diethyl ether with triethylsilane and Aluminum Chloride. Better yields of both alkyl and aryl aldehydes are obtained from mixtures of acyl chlorides or bromides and triethylsilane by using a small amount of 10% Palladium on Carbon catalyst (eq 7). This same combination of triethylsilane and catalyst can effect the reduction of ethyl thiol esters to aldehydes, even in sensitive polyfunctional compounds (eq 8). ... 

The flavane ring system is formed by the polyfunctional protein chalcone synthase from one molecule of a cinnamoyl CoA ester and 3 molecules malonyl CoA. The enzyme isolated from parsley (Petroselinum hortense) reacts with p-coumaroyl CoA and caffeoyl CoA as starter molecules (A 3.1). It uses the CoA esters as immediate substrates for the condensation reaction and contains neither an acyl carrier domain nor pantetheine. 

---