Magnesium cyclopropanolate

In the presence of a Lewis acid, alkyl 2-silyloxycyclopropanecarboxylates (14) react with a wide range of carbonyl compounds to give a diester (15), which has b n converted to a variety of furan derivatives (Scheme 18). An interesting use of the oxyanionic tautomer of a homoenolate involves the reaction of a magnesium cyclopropanolate (12) with the lithium enolate of cyclohexanone, from which a tricyclic ring containing a functionalized cycloheptanone (13) is formed in a single step (Scheme 18). ... 

Table 11.4. 1,2-Disubstituted cyclopropanols 22 from carboxylic acid esters 8 and 2-substituted ethyl-magnesium halides in the presence of titanium tetraisopropoxide or chlorotitanium triisopropoxide. Entry Starting Product Conditions Yield Ref. Ester R1 R3 [mol% (%) R2 Ti(OR)4] (d. r. Z/Eb) ...

This difficulty was overcome by first treating 3 with an equimolar amount of methyl-magnesium iodide, to convert it into a species, most likely the magnesium derivative 10, which did react with various organolithium reagents to give the expected 1-substituted cyclopropanols 11, Eq. (5)16,17>. 

For instance, the trimethylsilylbutadiynyl lithium derivative 12, resulting from the selective monodesilylation of bis-silylbutadiyne 18>, when treated with the magnesium salt 10 provided good yields of the 1-(trimethylsilylbutadiynyl) cyclopropanol 13, which was successfully used as a prostaglandin precursor, (vide infra, Sect. 5.5.2.1) Eq. (6)15). 

Since the hemiacetal 3, can now readily be prepared from cheap commercially available starting materials (vide supra, Eq. (1))7), this reaction constitutes a convenient source of 1-vinylcyclopropanols. Otherwise, the 1-ethynyl-cyclopropanols 9, also easily available from 3 or from its magnesium salt 10 (vide supra, Eq. (4) and (6) underwent either lithium aluminium hydride reduction in refluxing THF to lead exclusively to the E-1-vinylcyclopropanols 69 or reduction with dicyclopentadienyl-titanium hydride in ether at 0.°C, prepared from isobutylmagnesium halides and a catalytic amount of dicyclopentadienyl titanium dichloride (r -CjH TiCk), to yield exclusively the Z isomer 70, Eq. (22) 15,39). 

Methylmagnesium bromide Magnesium, bromomethyl- (8,9) (75-16-1) Diisopropylamine (8) 2-Propanamine, N-(l-methylethyl)- (9) (108-18-9) 2-Methyi-i-tetralone 1 (2H)-Naphthalenone, 3,4-dihydro-2-methyl- (8,9) (1590-08-5) Cyclopropanone ethyl hemiketal Cyclopropanol, 1-ethoxy- (8.9) (13837-45-1) Sodium hydride (8,9) (7646-69-7)... 

Aryl-1-cyclopropanols are prepared by a Grignard base elimination process [38 Eq. (31)]. The key step is ethoxide elimination from the magnesium alkoxide intermediate. The resulting cyclopropanone is then reacted with aryl lithiums to give the final product. 

A 1,3-deoxyhalogenation to give a cyclopropanol derivative 6 was accomplished by reaction of a chloroketal with magnesium in tetrahydrofuran. . ... 

A solution of methylmagnesium iodide in EtjO, prepared by the reaction of magnesium (243 mg, 10 mmol) and iodomethane (1.42 g, 10 mmol) in dry EtjO (40 mL), was cooled in an ice bath and triturated dropwise with 1-ethoxycyclopropanol (1.02 g, 10 mmol) in EtjO (20 mL). Methane evolved immediately and a white suspension of 4 was formed. This suspension of the reagent can be conveniently used for reactions with organolithium reagents, e.g. aryllithiums, to give 1-aryl-1-cyclopropanols. 

The nucleophilic addition of organoaluminum reagent 60 to the magnesium salt 57 provided the homopropargylic cyclopropanol 61 in 50% yield. ... 

Table 11.4. 1,2-Disubstituted cyclopropanols 22 from carboxylic acid esters 8 and 2-substituted ethyl-magnesium halides in the presence of titanium tetraisopropoxide or chlorotitanium triisopropoxide.

The ester Kulinkovich reaction was used to prepare a key allylic bromide 5333 in a synthesis of neolauh-malide and isolaulimalide (Scheme 5.88). The cyclopropanol 5.332 produced by the Kulinkovich reaction of ester 5.331, as its mesylate, was subjected to ring opening with magnesium bromide. This is likely to involve electrocyclic ring opening of the cyclopropyl carbocation, followed by bromide trapping. 

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