Generation and reactions of low-valent titanium alkoxide-acetylene complexes. A practical preparation of allyl alcohols

1,2-Additions of Organomagnesium Halides to Phosphaalkynes: Synthesis of 2-Phospha-1-vinylmagnesium Halides and a Novel Type of Magnesium-Phosphorus Cage Compound

“…In the course of our investigations on the use of metallocene [3] and η 8 -cyclooctatetraene trunk complexes [4] of zirconium and hafnium in the synthesis of new heterocyclic organophosphorus compounds, we attempted to use the di-(isopropoxy)(η 2 -propene)titanium complex [5] Ϫ readily accessible from titanium tetraisopropoxide and isopropylmagnesium chloride (2a) Ϫ as a starting material in an appropriate cyclooligomerization protocol of, for example, tert-butylphosphaacetylene (1). In these experiments we found that the Grignard reagent reacts with 1 at least as rapidly as with titanium tetraisopropoxide with the result that an inseparable mixture was obtained from the reaction.…”

Mechanism of the Kulinkovich Cyclopropanol Synthesis: Transfer‐Epititanation of the Alkene in Generating the Key Titanacyclopropane Intermediate

“…Similarly, decomposition of diisopropyltitanium() diisopropoxide (10) at low temperatures has been proposed to occur via the titanacyclopropane 11, the presumed source of Ti(OiPr) 2 (8) for various organic synthetic procedures used by Sato's group involving allylic halides, [7] olefins [13] or alkynes [14] (Scheme 2). In order to determine whether alkyltitanium 10 does decompose at Ϫ78°C or at higher temperatures to give the 2-methyltitanacyclopropane 11 [termed (η 2 -propene)Ti(OiPr) 2 by Sato, Scheme 4] two reactions were designed and carried out to chemically trap any of the intermediate 11 formed.…”

“…Diisopropyltitanium() diisopropoxide (10) has been shown to be kinetically stable in the temperature range of Ϫ78°C to ϩ25°C and hence we conclude that 10 does not decompose within this temperature range into the titanacyclopropane 11, as assumed in the work reported by the Sato group. [7,13,14] Reliable chemical trapping agents for titanacyclopropanes, such as esters and nitriles, failed to detect the presence of 11 when 10 was warmed from Ϫ78°C to ϩ25°C . Although 10 does not undergo the Kulinkovich cyclopropanol reaction with methyl benzoate (1a) below 25°C, it does form the cyclopropanol 19 slowly at room temperature (ca.…”

“…Scheme 2 This viewpoint is exemplified by the work of both the Sato group [7] and the Cha group. [8,12] Sato's approach uses mainly the isopropyl Grignard reagent to generate the putative Kulinkovich intermediate 11, via 10, with subsequent transfer of Ti(OiPr) 2 (8) presumably by ligand transfer to an allylic halide, [7] olefin [13] or to acetylene, [14] to form the titanometallics 12, 13 or 14, respectively (Scheme 2). Although the final titanium-free products formed by the hydrolysis or oxidation of, or the insertion of unsaturated substrates into, the σ(CϪTi) bonds are consistent with the presence of 12, 13 or 14 as precursors, the pathway of their formation via intermediates 10 and 11, and subsequent li- (15) [11,15,16] or indirectly by transfer-epititanation with R 2 TiL 2 (16) [17] to form three-membered titanocycles 17 have increased our understanding of the formation and reactivity of such metallocyclic intermediates (Scheme 3).…”

The Handy Use of Brown’s P2‐Ni Catalyst for a Skipped Diyne Deuteration: Application to the Synthesis of a [D4]‐Labeled F4t‐Neuroprostane

“…Since all attempts to isolate the required (Z,Z,Z)-triene 16 b were unsuccessful, the appealing titanium(II)-based methodology developed by Sato et al [26] seemed promising, in regard to its successful use by Kitching and Hungerford [27] in the synthesis of deuterium-labeled linolenic acids. The main feature of this convenient one-pot procedure is that the alkoxytitanium-acetylene complex intermediate generated in situ from TiA C H T U N G T R E N N U N G (OiPr) 4 (5.3 equiv) and iPrMgCl (13.8 equiv) in diethyl ether at À78 8C could provide direct access to both the reduced derivative 16 b and the deuterated compound 17 b by quenching with either H 2 O or D 2 O, respectively (Scheme 6).…”