Tetrasubstituted bis

Semi-empirical calculations for the geometry and dipole moment of tetrasubstituted bis-spiro-l,2,4-trithiolanes derived from adamantanethione were reported <2004JMT(668)179>. Satisfactory agreement with X-ray data was obtained with the PM3 method. 

SCHEME 31 Self-sensitized photooxygenation of tetrasubstituted bis(fulleride) derivatives 72. ... 

Similarly, irradiation of tetrasubstituted bis(fulleroid) derivatives 72 in the presence of oxygen affords a 12-membered ring diketone on the surface of the fullerene. In spite of the same 60 n electronic structure as C o, whose photooxygenation leads to the formation of the fullerene epoxide, [2 -I- 2]-cycloaddition of 72 with Oj followed by symmetrical ring opening of the dioxetane 73 predominantly occured to give 74 (Scheme On the contrary, oxidation and Diels-Alder reaction of the mother... 

Tetrasubstituted phosphinous amides of the type R2NPPh2 have been successfully arylated at phosphorus by the action of bromobenzene, in a process catalyzed by NiBr2, to give the aminophosphonium bromides [R2NPPh3] Br [109]. Other representative members of this class form phosphane-borane complexes [62], are aminated at phosphorus by chloramine to yield bis(amino)phos-phonium salts [110] and have been claimed to be protonated at phosphorus by ethereal tetrafluoroboric acid, as determined by NMR analysis [111]. 

In 2001, Furstner reported the preparation and characterisation of the NHC-Ru complex 22 containing iV,iV -bis[2,6-(diisopropyl)phenyl]imidazolidin-2-ylidene (SIPr) [29] (Fig. 3.6), which is the congener of complex 20. Subsequently, Mol and co-workers revealed that complex 22 was a highly active metathesis initiator [30]. More recent comparative studies showed that catalyst 22 could catalyse the RCM of 1 faster than any other NHC-Ru catalyst, while it was not stable enough to obtain complete conversion in the RCM of 3 and was inefficient for the construction of the tetrasubstituted double bond of cyclic olefin 6 [31]. 

Bis(diamino)alanes (R2N)2A1H were used for the hydroalumination of terminal and internal alkenes [18, 19]. TiCb and CpjTiCb are suitable catalysts for these reactions, whereas CpjZrCb exhibits low catalytic activity. The hydroaluminations are carried out in benzene or THF soluhon at elevated temperatures (60°C). Internal linear cis- and trans-alkenes are converted into n-alkylalanes via an isomerization process. Cycloalkenes give only moderate yields tri- and tetrasubstituted double bonds are inert. Hydroaluminahon of conjugated dienes like butadiene and 1,3-hexa-diene proceeds with only poor selechvity. The structure of the hydroaluminahon product of 1,5-hexadiene depends on the solvent used. While in benzene cyclization is observed, the reaction carried out in THF yields linear products (Scheme 2-10). 

Further investigation with various silyl ketene acetals is summarized in Table 6. Silyl ketene acetals derived from various esters were reacted with /V-benzyloxy-carbonylamino sulfones 1 in the presence of 0.5-1 mol% Bi(0Tf)3-4H20. The corresponding (3-amino esters 24 were obtained in moderate to good yields (Table 6). Silyl enolates derived from esters as well as thioesters reacted smoothly to give the adducts. The /V - be n z v I o x v c ar bo n v I a m i n o sulfone derived from n-butvraldehyde lp led to moderate yields of (3-amino esters when reacted with (thio)acetate-derived silyl ketene acetals (Table 6, entries 1 and 2). A very good yield was obtained when the same sulfone was subjected to a tetrasubstituted silyl ketene acetal (Table 6, entry 3). The latter afforded moderate to good yields of (3-amino esters 24 with phenylacetaldehyde, / -tolu aldehyde, and o-tolualdehyde-derived sulfones (Table 6, entries 4-6). 

An intramolecular substitution of trimethylamine fix>m 17 gave a bicyclic oxetane 18 in a diastereoselective process <98MI2185>. A [2+2]cycloaddition of 2,2,4,5-tetrasubstituted 2,3-dihydrofuran to aryl aldehydes gave the bicyclic oxetane 19 <98JCS(P1)3261>. 2,2-Disubstituted-3-bromooxetane was obtained by a 4-endo-tcig cyclization process of 3,3 -disubstituted allyl alcohol in the presence of bis(collidine)bromine hexafluorophosphate <99JOC81>. 

Although the mechanism of the transformation of single into double bonds has not been investigated in detail, a heteroatom attached to the single bond is necessary for an efficient introduction of the double bond. Trisubstituted pyrazo-lines 46 can be oxidized with (diacetoxyiodo)benzene 3 to the corresponding pyrazoles 47 in good yields [98]. Two double bonds can be introduced in easy accessible proline derivatives 48 [99] by an oxidative decarboxylation with [bis(trifluoroacetoxy)iodo]benzene 4 yielding tetrasubstituted pyrroles of type 49, Scheme 22 [100]. 

The Heck reaction of 1,3 -diene systems via 7r-allylpalladium is also useful. This cyclization, which forms very congested quaternary carbon centers involving the intramolecular insertion of di-, tri- and tetrasubstituted alkenes, is particularly useful for natural products synthesis. In the synthesis of morphine, bis-cyclization of the octahydroisoquninoline precursor 112 by the intramolecular Heck reaction proceeded using palladium trifluoroacetate and 1,2,2,6,6-pentamethylpiperidine (PMP). The insertion of the diene system forms the 7i-allylpalladium intermediate 113, which attacks the phenol intramolecularly to form the benzofuran ring 114. Based on this method, the elegant total syntheses of (—)- and (+)-dihydrocodeinone, and (—)- and (+)-morphine (115) have been achieved [50],... 

When lithium methanetellurolate was used, l,I-bis[methyltelluromethyI cyclopropane was isolated instead of the expected tetrasubstituted methane derivative1. 

A series of tetrasubstituted thiazole derivatives 28 has been prepared via a multi-component tandem protocol <07T10054>. Reaction of bis(aroylmethyl)sulfides 23 with aryl aldehydes and ammonium acetate in 1 2 1 ratio under solvent-free microwave irradiation affords 28 in good yields. This reaction presumably starts with Knoevenagel condensation of sulfide with 2 equiv. of aryl aldehydes to give 24. Michael addition with ammonia and concomitant cyclocondensation lead to 26. Base-catalyzed ring opening of 26 to 27 and ring... 

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