Regiospecific reactions

Ester, ether, and cycHc acetal groups are used as blocking groups to allow regiospecific reactions to take place, ie, reaction at specific unblocked hydroxyl groups. 

Alkyl-5-arylisoxazoles (303) were prepared by the regiospecific reaction of appropriate 1,3-diketones (302) (R = alkyl or perfluoroalkyl) with hydroxylamine hydrochloride in pyridine (79MI41601). 

Alkyl(or 3-aryl)-5-methylisoxazoles (306) were prepared by the regiospecific reaction of phosphonium salts (304) with hydroxylamine, followed by the treatment of the resulting isoxazole-containing phosphonium salts (305) with aqueous sodium hydroxide (80CB2852). 

Stereosperificity Regiospecificity Reaction specificity Reduced disposal costs... 

Ruppe S, A Neumann, W Vetter (2003) Anaerobic transformation of compounds of technical toxaphene. I. Regiospecific reaction of chlorobomanes with geminal chlorine aroms. Environ Toxicol Chem 22 2614-2621. 

Regiospecific reactions occur between unsymmetric diamines and un-symmetric vinamidinium salts [81JCR(S)356 81JCS(P1)726]. 

Note that the terms regiose-lective and regiospecific, however, are defined in terms of each other. A regiospecific reaction is one that is 100% regioselective. 

Zinc(II) chloride, bromide and iodide were found to ring open iV-tosyl-2-phenyla-ziridines forming the tnms-/3-haloamine in a regiospecific reaction at the benzylic carbon of the aziridine ring.51 In the absence of a benzylic carbon, the halide ion attack was mainly at the least substituted carbon of the ring. 

The regiospecific reaction of the cyclic sulfate 47 with AcSK or KSCN gives acetylthio or thiocyano sulfates, which have been converted to the episulfide 48 by treatment with NaOMe (Scheme 11) <1995CC461, 1997JOC3944>. Similar double displacement with KSeCN affords the selenocyanate, which has been reduced to the corresponding alkene 49 by sodium borohydride in methanol (Scheme 11) <1995CC461, 1997JOC3944>. 

A new approach to 1,2,4-thiadiphospholes 129 via a regiospecific reaction of phosphaalkynes 128 with sulfur in the presence of the polymeric thiotantalum(v) sulfide [STaC ] was reported by Regitz and co-workers (Equation 12) <2002EJ01664>. 

The procedure of exp. 12 exemplifies the regiospecific reaction of dilithiated isopropenyl acetylene with carbonyl compounds. This example is significant in that the coupling product is a precursor of an aggregation pheromone of the baric beetle treatment with activated zinc powder in ethanol gives ipsenol H2C=CHC(=CH2)CH2CH(OH)CH(CH3)2 in almost quantitative yield. [46]... 

When this reaction is run in the laboratory, the only product formed is 2-chloropropane. No 1-chloropropane is observed. A reaction such as this one that produces only one of two possible orientations of addition is termed a regiospecific reaction. (A reaction that produces predominantly one possible orientation but does form some of the product with the other orientation is termed a regioselective reaction.)... 

Regiospecific reaction (Section 11.2) A reaction that produces only one of two possible orientations (regiochemistries) in a reaction. 

Regiospecific Reaction Catalyzed by Immobilized C. antarctica Lipase Irimescu et al. (2001, 2002) recently established a reaction system ... 

Such a reaction path is explained by regiospecific reaction of the intermediately formed ambident anion with the esters of nitrous acid [518],... 

Once single zirconacyclopentadienes 20 are formed, only the regiospecific reaction of one carbon-zirconium bond with an electrophile could lead to the stereoselective preparation of metalated dienes 26 (Scheme 13). 

On the contrary, once unsymmetrical zirconacydopentadiene 20 (Scheme 13) is obtained regiospecifically, the formation of stereodefined metalated dienyl zirconocenes 26 requires a regiospecific reaction of only one carbon-zirconium... 

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