Titanium generation

An 80% yield of tetraphenylfuran is obtained by treatment of benzoyl chloride with active titanium generated by lithium aluminum hydride reduction of titanium trichloride (Scheme 84e) (8UOC2407). The reaction nroceeds via benzil and tetraphenylbut-2-ene-l,4-dione, both of which are minor products of the reaction. 

Reductive elimination from 2-en-l,4-diol derivatives has been used to generate 1,3-dienes. Low-valent titanium generated from TiCl3-LiAlH4 can be used directly with the diols. This reaction has been used successfully to create extended polyene conjugation.305... 

Fiirstner has discovered that a low-valent titanium generated by pretreatment of titanium powder with Me3SiGl or Et3SiGl is effective for the McMurry coupling vide infra) ... 

Reduction of l92-dibromides. Chlorobis(cyclopentadienyl)titanium, generated in situ by zinc reduction of (C5H5)2TiCl2 in THF, effects rapid reductive denomination of vic-dibromides to alkenes by an anft-elimination.1 Examples ... 

An alternative procedure for the preparation of diethyl cyanobenzylphosphonates uses the addition of diethyl trimethylsilyl phosphite to P-nitrostyrenes in the presence of TiCl4. The silyl functionality is transferred to the oxygen to form nitronates, which, in the presence of low-valence titanium generated in situ, are converted to diethyl cyanobenzylphosphonates in 74-91% yields (Scheme 6.19). s ... 

The diacetylene 15 readily underwent Diels-Alder cycloaddition with furan to furnish the endoxide 16, which was hydrogenated catalytically to the tetrahydro compound 17. Dehydration of 77 with polyphosphoric acid gave 1 in 16% yield (Eq. 7) Alternatively, deoxy nation of 16 with low valent titanium generated by reducing titanium tetrachloride with lithium aluminium hydride also afforded 7 in 50% yield... 

The reductive coupling of phthalimides with ketones and aldehydes in THF by low-valent titanium generated from Zn-TiC gave 3-hydroxy-3-(l-hydroxyaIkyl)-isoindolin-l-ones as two-electron reduced products and alkyhdene-isoindolin-l-ones as four-electron reduced products. These could be obtained selectively by controlling the reaction conditions. The geometric ratios of the alkylideneisoindolin-l-ones obtained from phthalimides and aldehydes could be increased by reflux in PPTS/ toluene (catalyst). In particular, the Z-isomers of A-unsubstituted alkylideneisoindolin-l-ones could be obtained exclusively. 

Sodium sulfide reacts with two equivalents of a 2-halo-ketone to generate an a,a -thiobisketone, e.g. 37, and these can be cyclised to give aromatic thiophenes [100] via an intramolecular pinacol reaction promoted by low valent titanium, generated in situ, followed by the elimination of two equivalents of water, for example, from 37 to 39 via 38 (Scheme 63) [101]. 

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