A-Benzylidines

NIS, 2.5 eq., CH3CN, h. This method cleaves a benzyl group in carbohydrates, provided that there is an adjacent hydroxyl. In some cases a benzylidine is formed. ... 

In the presence of a neighboring hydroxyl, DDQ cleavage results in the formation of a benzylidine acetal, which, upon extended treatment with DDQ, gives a hydroxy benzoate that can be hydrolyzed with LiOH (DDQ (4.0 eq.), CH2CI2 buffer pH 7.0 (1 1), 0-25°C, 4 h LiOH 2.0 eq.), MeOH, 25°C, 12 h, 85% over two steps)." ... 

One specific example illustrating the utility of nitroalkylations was reported by Drew, et af.,113 and is shown in Scheme 2.6.1. In this report, a benzylidine protected glucose analog was converted in a 69% yield to a p-C-... 

On the other hand, cyclic ketones react well with nonenolizable aldehydes (equations 64-66). - As shown in equation (65), mild conditions lead to the aldol (as a diastereomeric mixture). More forcing conditions provide the a-benzylidine derivatives (equations 64 and 65). By adjusting the stoichiometry, a,a -bisarylidine derivatives may be obtained in excellent yield from cyclohexanone or cyclopentanone (e.g. equation 66). ... 

Coxon and Stoddart have directed their attention to the formation of penta-erythritol-derived cryptands. With these molecules, the strategy was to block one pair of hydroxyl groups as an acetal and form a crown from the remaining diol. In the first of the two reports cited above, this was accomplished by treating the 0-benzylidine derivative of pentaerythritol with base and diethylene glycol ditosylate. The crown was then treated with a mixture of UAIH4 and BF3 which gives partial reduction of the acetal as shown in (8.9), above. The monoprotected diol could now be treated in a fashion similar to that previously described and the benzyloxy cryptand (77) would result. The scheme is illustrated below as Eq. (8.10). 

Several variations of Makosza s procedure have been recorded using different catalysts. Generally, because of the need for the slow release of the dichlorocarbene in the presence of the reactive substrate, the weaker catalysts are preferred. There seems, however, to be some advantage in the use of multisite ammonium salts, e.g. 2-benzylidine-Ar,Ar,MA,.A,Ar -hexaethylpropane- 1,3-diammonium dichloride, PhCH=C(CH2NEt3)22+ 2CE, although yields and rate of reaction are not significantly better than those of Makosza s procedure [6, 7]. 

The autoxidation of azlactones under basic conditions provides a convenient route to diacylamines [13]. Yields are usually >80%, except for the benzylidine derivatives, which are hydrolysed to the acylaminoacetic acids (Scheme 10.8). 

An extensive review of the hetero-Diels-Alder reactions of 1-oxabuta-1,3-dienes has been published. Ab initio calculations of the Diels-Alder reactions of prop-2-enethial with a number of dienophiles show that the transition states of all the reactions are similar and synchronous.Thio- and seleno-carbonyl compounds behave as superdienophiles in Diels-Alder reactions with cyclic and aryl-, methyl-, or methoxy-substituted open-chain buta-1,3-dienes.The intramolecular hetero-Diels-Alder reactions of 4-benzylidine-3-oxo[l,3]oxathiolan-5-ones (100) produce cycloadducts (101) and (102) in high yield and excellent endo/exo-selectivity (Scheme 39). A density functional theoretical study of the hetero-Diels-Alder reaction between butadiene and acrolein indicates that the endo s-cis is the most stable transition structure in both catalysed and uncatalysed reactions.The formation and use of amino acid-derived chiral acylnitroso hetero-Diels-Alder reactions in organic synthesis has been reviewed. The 4 + 2-cycloadditions of A-acylthioformamides as dienophiles have been reviewed. ... 

Oxidation of several 1,1-bisphenols 78 with IBD gives spirobenzofuran derivatives of general formula 79 (Eq. 21). This approach, when applied to benzylidine l.l -bisnaphthols 80, leads to a stereospecific cyclization, thereby forming the less hindered naphtho[2,l-fi]furan-2(l//)-spiro-r-(2//)-naphthalene-2 -ones (82) [80JCS(P1)1978,80JCS(P1)1986]. The conversion 80 to 82 probably occurs through intermediate 81 (Scheme 25). 

Di-(a-azidobenzylidene)-azine see Bis (a-azido-benzylidine)-azine 2 B133... 

Substituted aldehydes and substituted amines also react for example, the sodium salt of a-naphthylamine 4-sulphonic acid when dissolved in water and shaken with an alcoholic solution of benzaldehyde yields sodium benzylidine naphthionate. 

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

The 2-hydroxyl of methyl 4,6-<9-benzylidine-a-glucopyranoside was selec-s tively protected.7... 

There is complete parallelism here with strychnine thus, dihydro-vomicine gives an 11-benzylidene derivative (196). Deoxyvomicine (CCXLII) gives a product which may be the simple benzylidine compound CCXLIII or the rearranged a-pyridone CCXLIV (197) deoxy-dihydrovomicine behaves similarly. 

The interest in the mechanisms of SchifF base hydrolysis stems largely from the fact that the formation and decomposition of SchifF base linkages play an important role in a variety of enzymatic reactions, for example, carbonyl transfers involving pyridoxal phosphate, aldol condensations, /3-decarboxylations and transaminations. The mechanisms for the formation and hydrolysis of biologically important SchifF bases, and imine intermediates, have been discussed by Bruice and Benkovic (1966) and by Jencks (1969). As the consequence of a number of studies (Jencks, 1959 Cordes and Jencks, 1962, 1963 Reeves, 1962 Koehler et al., 1964), the mechanisms for the hydrolysis of comparatively simple SchifF bases are reasonably well understood. From the results of a comprehensive kinetic investigation, the mechanisms for the hydrolysis of m- and p-substituted benzylidine-l,l-dimethylethylamines in the entire pH range (see, for example, the open circles in Fig. 13) have been discussed in terms of equations (23-26) (Cordes and Jencks, 1963) ... 

A 0. IM solution of the Step 3 product dissolved in CH2CI2 was charged into a Schlenk tube followed by a CH2CI2 solution of bis(tricyclohexylphosphine)benzylidine ruthenium(IV)dichloride (0.04 eq). The solution was then stirred for 14 hours at ambient temperature. Excess ethylvinyl ether was added, and the solution was stirred while exposed to the atmosphere for 30 minutes. Thereafter the polymer was precipitated into cold diethyl ether, and the product was isolated in 75% yield. 

---