Regioselectivity conversion

Lithium perchlorate-diethyl ether promotes the chemo- and regioselective conversion of epoxides to carbonyl compounds (e.g., 126 127), a reaction which is thought to proceed via... 

The Peterson olefination reaction involves the addition of an a-silyl substituted anion to an aldehyde or a ketone followed by the elimination of silylcarbinol either under acidic (awP -elimination) or basic (syn-elimination) conditions to furnish olefins178. Thus, Peterson olefination, just like Wittig and related reactions, is a method for regioselective conversion of a carbonyl compound to an olefin. Dienes and polyenes can be generated when the Peterson reaction is conducted using either an ,/l-unsaturated carbonyl compound or unsaturated silyl derivatives as reaction partners (Table 20)179. 

Acylbenzotriazoles 162 are efficient C-acylation reagents for the regioselective conversion of ketone enolates into P-diketones . Diethyl(l-benzotriazolmethyl)phosphinate (163) was found to be a convenient reagent for the stereoselective preparation of (E)-l-(l-alkenyl)benzotriazoles <00SC1413>. The novel three-carbon synthon 1-(1//-133-... 

Scheme 13.29. Regioselective conversion of 1-vinylcyclopropyl carbonate into alkylidenecydopropane derivatives.

Scheme 27 I -mediated regioselective conversion of a diamide to an enamide with subsequent aziridine formation and methanolysis.

Dealkylations have been used in the regioselective conversion of methoxyaryl groups to phenols in natural products, particularly alkaloids 1471 such as papaverine (30), and in the production of mammalian metabolites by microbial biotransformation, as exemplified by the biotransformation of bisprolol (4). 

Direct regioselective conversion of a variety of cyclic and acyclic ketones to a-fluoro ketones was achieved in high to excellent yield using NFTh (21) in acetonitrile solution.96 The collected results (Table 10) of this highly effective direct transformation show that a comprehensive range of ketones can be fluorinated a to the carbonyl group, without prior activation. 

This section outlines three chemical transformations designed to allow further synthetic elaboration of the diols obtained from AD. The first and most broadly applicable method is the conversion of the diols into cyclic sulfates, a functionality that has reactive properties like an epoxide but is even more electrophilic than an epoxide [68]. The second approach to diol activation is the regioselective conversion of one of the hydroxyl groups into a sulfonate ester [69], This approach requires that the diol be substituted in a way that leads to regioselective derivatization of one of the two hydroxyl groups, and diol esters are a prime example of such... 

Sodium dithiocarbamates are similarly converted to aryl dithiocarbamates with polymeric aryliodonium bisulfates 20 derived from styrene (Scheme 41) [116]. The high regioselectivity of C-I bond cleavage in 20 is noteworthy, only trace amounts of iodoarenes [Arl] having been detected in occasional cases . Regioselective conversions of p-phenylenebis(phenyliodonium) ditriflate (21) top-phenylenebis(dithiocarbamates) with dithiocarbamate salts have also been reported (Scheme 41) [117]. 

A catalytic, completely regioselective conversion of 4,4-dimethyl-2-pentyne (methyl-r-butylacetylene) to 2,5-di(r-butyl)-3,4-dimethylcyclopentadienone is mediated by (PhCN)2PdCl2. Other examples exist for early as well as late transition metals, and an isonitrile has been used as a CO equivalent in one Ni -based system as well, Finally, a heterogeneous catalytic intramolecular cycloaddition of diynes has been developed, leading to cyclopentadienones which either dimerize (Diels-Alder) or in certain cases may be trapped by nucleophiles (equation 10). °... 

The greater activity of LiC104 (3 mol %)-CH2Cl2 enables conjugate addition of Si-2 to 12. Complete and regioselective conversion to the desirable 1,4-adduct was, in fact, achieved within 1 h >91 % isolated yield), presumably via a group transfer-type process (Sch. 60) [72]. 

Enones. Regioselective conversic accomplished with this reagent combinaiki... 

Enones. Regioselective conversion of silyl enol ethers to enones is readily accomplished with this reagent combination. 

Erythrose derivatives such as 2-4, with a free hydroxy function, offer many possibilities for regioselective conversions in addition, the free hydroxy group in 2 or 3 does or may influence the regio- and stereoselectivity of additions to the carbonyl group. 2,4-O-Ethylideneerythrose, because of its di- or oligomeric form, is configurationally stable at room temperature and can be stored for several months at room temperature.9-18... 

Bajwa, J.S., and Anderson, R.C., A highly regioselective conversion of epoxides to halohydrins by hthium halides, Tetrahedron Lett.. 32, 3021, 1991. 

Hydrostannylation. Regioselective conversion of 1-alkynes to 2-tributylstannyl-l-alkenes is accomplished with BuySnH in the presence of (r-BuNC)3Mo(CO)3/ By changing the catalyst to (p-02NC6H4NC)3W(C0)3 propargyl acetate furnishes a distannylated product. ... 

Other papers of interest in this section report addition of arylsulphenyl chlorides to c/5-2,6-dimethylocta-2,6-diene,the mild regioselective conversion of the epoxide (72) into (73) using [Fe2(CO)9], allylboration of citral, ... 

New methods in organic synthesis. Parti. Regioselective conversion of ketones into olefins via vinyl triflates. Part II. An approach to the total synthesis of morphine... 

A regioselective conversion of 6,8-dioxabicyclol3.2. IJoctanes to oxepanes is effected by a TiCl4-catalyzed reduction with EtiSiH. ... 

AUylic chlorides (4, 552). This system is useful for regioselective conversion of allylic alcohols into allylic chlorides. The method, however, is not so useful for preparation of allylic chlorides with boiling points near those of carbon tetrachloride (77°) and chloroform (62°). The isolation of the product can be simplified by use of hexachloroacetone (b.p. 202°) rather than carbon tetrachloride. Yields and regioselectivity are still high in this variation. ... 

Strategy of Rh-triggered qrcloaddition cascade. In this case, the Rh-catalyzed transformation of a-diazoketone 132 into an oxatetracycUc key cycloadduct 133 through intramolecular [3+2]-cycloaddition of an in-situ generated carbonyl yUde was achieved. Further, the regioselective conversion of the cycloadduct 133 into a tropolone derivative led to an efficient enantioselective access to colchicine (Scheme 40). 

Aza-di-n-methane (ADPM)- rearrangement reactions of both 1-aza- and 2-aza-1,4-dienes are known but not so common at the present time. Nevertheless, and largely due to the work of Armesto et a/., the potential utility of such processes is becoming clearer. In the case of ADPM rearrangement reactions involving 1-aza-1,4-dienes, regioselective conversions are observed with, for exanple, the oxime 23 being converted into cyclopropane 24 in 74% yield after irradiation under triplet-sensitized conditions for just 30 min fScheme 9.S1. 

A major part of regioselective conversions comprises additions to unsymmetrically substituted alkenes, substitutions in al-lyhc positions or in aromatic compounds, conversions of anions, radicals, or carboca-tions with two reactive sites, and reactions at different CH bonds. 

The unexpected regioselective conversion of (95) to (99) on treatment with Bu OK in DMSO has been attributed to nucleophilic attack of either dipolar oxygen on dimethyl sulfoxide, or dimsyl anion on the trivalent sulfur cation of (95) to form sulfurene intermediates (96) or (97), respectively. ... 

Phung C, Pinhas AR (2010) The high yield and regioselective conversion of an unactivated aziridine to an oxazolidinone using carbon dioxide with ammonium iodide as the catalyst Tetrahedron Lett 51 4552-4554... 

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