Scheme 2. Johnsons method

The silyl-Hilbert-Johnson method of nucleoside synthesis, using trimethylsilyltriflate as catalyst, is useful for the preparation of N-3 nucleosides (e.g., from 4-carbamoylimidazolium-5-olate) <84JHC529>, and a similar silyl displacement method has been used to make 1-alkylthio- and 1-phenylthio-l-trimethylsilyloxyalkanes and -cycloalkanes. This latter process uses 1-trimethyl-silylimidazole (177) and trimethylsilyltriflate as catalyst <84CHE662, 90S104>. The use of two equivalents of the thiol prevents the formation of imidazole adducts (Scheme 116) <90S104>. 

A salient structural feature of intermediate 18 (Scheme 2b), the retrosynthetic precursor of aldehyde 13, is its y,r5-unsaturated ester moiety. As it turns out, the Johnson ortho ester variant of the Clai-sen rearrangement is an excellent method for the synthesis of y,<5-unsaturated esters.11 In fact, the Claisen rearrangement, its many variants included, is particularly valuable in organic synthesis as a method for the stereocontrolled construction of trans di- and tri-substituted carbon-carbon double bonds.12,13 Thus, it is conceivable that intermediate 18 could be fashioned in one step from allylic alcohol 20 through a Johnson ortho ester Claisen rearrangement. In... 

The second synthesis of the enantiomer of this sulfone entails two transformations. First, (-)-a-naphthyl p-tolyl [ 0] sulfoxide 141 was converted into the corresponding [ 0] sulfoxide 141 by the method of Johnson (with inversion of configuration). Its oxidation with m-chloroperbenzoic acid afforded the chiral sulfone (+)-142 (Scheme 8). The latter procedure was also used for the preparation of chiral (-)-[ H2lbenzyl p-tolyl [ 0 0]sulfone (143) from (-)-[ H2] benzyl p-tolyl sulfoxide 37. 

Of great importance was the discovery by Johnson et al. (185) of the stereospecific synthesis of optically active sulfonimidoyl chlorides, which are key substrates for making new types of sulfonimidoyl compounds. The method involves chlorination of readily available chiral sulfinamides with chlorine or A/-chlorobenzotriazole. Scheme 12 summarizes the synthesis of (-)-(/ )-A/-methylphenylsulfonimidoyl chloride 163 from (+HS>N-methyl benzenesulfinamide 164 and its reactions with sodium phenoxide and dimethylamine. 

Johnson and McCants (161) were the first to show that the alkaline hydrolysis of alkoxysulfonium salts, obtained by 0-alkylation of sulfoxides, proceeds with inversion of configuration at sulfur. This method was employed to interconvert (/ )- and (5)-benzyl p-tolyl sulfoxides 37 as shown in Scheme 21. In contrast to the hydroxide anion, the chloride, bromide, and iodide anions as well as the nitrogen atom of pyridine react with chiral ethoxydiarylsulfonium salts, not at sulfur but at the a-carbon atom of the ethoxy group, yielding the starting sulfoxide with retained configuration (284). On the other hand, the nucleophilic attack of the fluoride anion is directed at sulfur as in the case of the hydroxide anion (285). 

It is worth noting that in this synthesis of Cecropia juvenile hormone a strategy which is the reverse of the one developed by W.S. Johnson [8] for the synthesis of steroids and other fused polycyclic systems bearing cyclohexane rings is used. This method involves a non-enzymatic cyclisation of a polyunsaturated intermediate with the appropriate stereochemistry (all-trans) (Scheme 13.3.6). Such cyclisation occurs with a really amazing stereoselectivity and several new chiral centres with the correct stereochemistry are created in one single step ... 

Monoazaporphyrins were first prepared using [2 4- 2] dipyrromethane condensation methods by Fischer et al.2 Later, Johnson et al. improved the yield to a moderate level ( 58%) by cyclization of 1,19-dibromobiladiene-a,c with NaN3.177 Syntheses of metallomonoazaporphyrins via oxophlorin intermediates have also been reported (Scheme 51),2,181... 

Stoichiometric sulfur ylide epoxidation was first reported by A.W. Johnson [23] in 1958, and subsequently the method of Corey and Chaykovsky has found widespread use [24-26]. The first enantioselective epoxidations using stoichiometric amounts of ylide were reported in 1968 [27, 28]. In another early example, Hiyama et al. used a chiral phase-transfer catalyst (20 mol%) and stoichiometric amounts of Corey s ylide to effect asymmetric epoxidation of benzaldehyde in moderate to good enantiomeric excess (ee) of 67 to 89% [29]. Here, we will focus on epoxidations using catalytic amounts of ylide [30-32]. A general mechanism for sulfur ylide epoxidation is shown in Scheme 10.2, whereby an attack by the ylide on a carbonyl group yields a betaine intermediate which collapses to yield... 

Reaction with an alkyl halide, catalysed with silver oxide, can be used not only for the preparation of ethers (see Scheme 4.11, p. 64) but also for the preparation of esters prior to GC analysis. Johnson and Wong [134] performed this reaction in a trapping column, specially adapted, packed with AgjO reagent, where they trapped the acids being analysed. They applied the method to the analysis of volatile acids in mutton. 

Reductive elimination of /i-hydroxysulfoximines provided the basis for a related olefination method put forward by C.R. Johnson and coworkers [91 ] (Scheme 64). 

Extremely useful ramifications of the Claisen rearrangement emerged with Johnson s discovery of the orthoester variant of this transformation. His approach (Scheme 2.156) involved the following sequence of steps, which were carried out in one reaction vessel (i) transesterification of the orthoester with an allylic alcohol to give 490 (ii) elimination to form the intermediate ketene acetal 491 and (iii) [3,3] sigmatropic rearrangement to yield the y, -unsaturated ester 492. The Johnson-Claisen procedure is properly considered to be one of the most efficient methods available to prepare y,(5-unsaturated esters such as 492. ° ... 

In 1973, Johnson reported the use of (N-methylphenylsulfonimidoyl)methyllithium (26) for addition to carbonyls, followed reductive elimination to produce the methylene derivative (28 Scheme 7). As with the Tebbe and Oshima procedures discussed in Sections 3. l.S and 3.1.6, this method can be applied to enones, ketones and, with comparatively diminished efficiency, aldehydes. The anion appears to be more nucleophillic than methylenetriphenylphosphorane, and there are several examples, detailed below, in which the Wittig reaction failed but the Johnson procedure succeeded. The addition and reductive cleavage can be combined into a single operation without isolation of the p-hydroxysulfoximine. ... 

In the Claisen-Johnson or Claisen-Eschenmoser variation, this reaction is a standard method for elongating a carbon chain by a terminally functionalized C2-fragment (normally from an orthoester or orthoamide). The preparative value lies in the mechanism-controlled transformation of 0-chirality to C-chirality under allylic transposition [reactions (17 to 20) in Scheme 7] [22]. As the rear-... 

Approximate DFT approaches have been available for many decades. The most well known method to inorganic chemists is probably the Xa method first introduced by Slater and Johnson [15]. The Xa scheme utilises only the exchange part of the Local Density Approximation (9). 

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