Titanium tetrachloride catalyzed

In the presence of allyltrimethylsilane, titanium tetrachloride catalyzed the ring cleavage of the tetrahydro-l,5-dioxa-3a-aza-pentalen-4-ones 79 giving the oxazolidinones 80 (Equation 33) <2001T5393>. 

Hansen and colleagues177 used (+)-pantolactone as a chiral auxiliary to achieve asymmetric induction in the first step toward their synthesis of d.v-perhydroisoq uinol inc 278. The titanium tetrachloride catalyzed reaction between 1,3-cyclohexadiene (275) and chiral acrylate 276 proceeded with high diastereofacial selectivity to give 277 (94% de) in 75% yield (equation 77). 

An example of a chelation-controlled titanium tetrachloride-catalyzed aldol condensation has been featured in a recent synthesis of pestalotin (eq. [86]) (100). The condensation illustrated afforded... 

The action of water in the titanium tetrachloride catalyzed polymerization is paradoxical, since water at —60 to —80° was present only in the solid phase its solubility in hexane at these temperatures is in the order of 10-10 moles per liter (Plesch et al., 83). It was found to be essential that the water be present as an extremely fine dispersion such as might result from the rapid bubbling of moist air through the liquid at the low temperature. Addition of liquid water which formed lumps of ice in the reaction mixture did not initiate polymerization. It may be concluded that a fine dispersion is necessary in order that reaction with titanium tetrachloride can occur and a chain reaction is initiated ... 

The reactivity profiles of the boronate complexes are also diverse.43 For example, the lithium methyl-trialkylboronates (75) are inert, but the more reactive copper(I) methyltrialkylboronates (76) afford conjugate adducts with acrylonitrile and ethyl acrylate (Scheme 16).44 In contrast, the lithium alkynylboronates (77) are alkylated by powerful acceptors, such as alkylideneacetoacetates, alkylidene-malonates and a-nitroethylene, to afford the intermediate vinylboranes (78) to (80), which on oxidation (peracids) or protonolysis yield the corresponding ketones or alkenes, respectively (Scheme 17).45a Similarly, titanium tetrachloride-catalyzed alkynylboronate (77) additions to methyl vinyl ketone afford 1,5-diketones (81).4Sb Mechanistically, the alkynylboronate additions proceed by initial 3-attack of the electrophile and simultaneous alkyl migration from boron to the a-carbon. 

In all instances a 2 1 mixture of anomers was obtained with the 3-D anomer predominating over the a-D anomer. The synthesis of 4 -acetamidoadenosine has been accomplished by the condensation of 4-acetamido-l,5-di-0-acetyl-2,3-di-0-benzoyl-4-deoxy-D-ribofuranose with chloromercuri-6-benzamido-purine using a titanium tetrachloride catalyzed reaction. ... 

Aqueous inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid and, preferentially, sulfuric acid, as well as some Lewis acids, e.g. boron trifluoride etherate and titanium tetrachloride, catalyze the a-addition of the isocyanides, yielding the a-hydroxycarboxamides (24) in 12-88% The catalysis of this reaction by acids is due to an enhancement of the electrophilic reactivity of the carbonyl compound (4). 

S-enaminone 282. The latter then undergoes cydization to ethyl-4-amino-2,3-dihydro-6-methylthieno[2,3-i ]pyridine-5-carboxylates 283 as proposed above. Titanium tetrachloride catalyzes not only the addition of acetoacetic ester to the nitrile group (the first step) but also the last stage of cydization (the formation of the C-N bond Scheme 61) (93LA1269). 

There are several strategies that involve the use of transition metal catalysts in addition to the Mukaiyama reaction. Reaction of leucinal with 1,3-butanediol gave a mixture of 6.115 (in 9% yield) and 6.116 (in 71% yield). After the chromatographic separation of 6.116, the titanium tetrachloride catalyzed reaction with 3-trimethylsilyl-l-propene gave 6.117. Ozonolysis and oxidation gave lactam 6.118, which was converted to 6.101a in five steps (overall yield was 32% from 6.117). 

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