Elimination of beta-thioalkoxy alcohols under Mitsunobu conditions. A new synthesis of conjugated enynes from propargylic dithioacetals

Treatment of propargylic dithiolanes 1 with (n)BuLi followed by a carbonyl electrophile yields the corresponding homopropargylic alcohol 3. Upon treatment with 2 equiv of PPh3 and DIAD, elimination of SR and OH moieties from 3 affords the corresponding olefins 4 in moderate to good yield. The reaction can be considered an alternative of McMurry coupling of two different carbonyl equivalents.     

Novozym-435-catalyzed enzymatic separation of racemic propargylic alcohols. A facile route to optically active terminal aryl propargylic alcohols

Novozym-435 (a form of Candida antarctica lipase B) was found to be an effective biocatalyst for the kinetic resolution of a variety of racemic terminal aryl propargylic alcohols affording highly optically active (S)-propargylic alcohols and (R)-propargylic alcohol acetates in high yields and good ees. The advantages of this reaction are the easy availability of starting materials and the biocatalyst, simple reaction conditions, easy operation and high stereoselectivity.     

A general procedure for the synthesis of enones via gold-catalyzed Meyer-Schuster rearrangement of propargylic alcohols at room temperature

Meyer-Schuster rearrangements of propargylic alcohols take place readily at room temperature in toluene with 1-2 mol % PPh(3)AuNTf(2), in the presence of 0.2 equiv of 4-methoxyphenylboronic acid or 1 equiv of methanol. Good to excellent yields of enones can be obtained from secondary and tertiary alcohols, with high selectivity for the E-alkene in most cases. A one-pot procedure for the conversion of primary propargylic alcohols into β-arylketones was also developed, via Meyer-Schuster rearrangement followed by Pd-catalayzed addition of a boronic acid.     

A new convenient synthesis of propargylic fluorohydrins and 2,5-disubstituted furans from fluoropropargyl chloride

Fluoropropargyl chloride reacted with carbonyl compounds to give propargylic fluorohydrins under mild conditions and in good yields; however, at higher temperatures and longer reaction times, 2,5-disubstituted furans are obtained, also in good yields. Fluorohydrins can be readily oxidized to alpha-fluoroketones and alpha-fluorocarboxylic acids with Jones' reagent.     

A general and stereoselective method for synthesis of tri- and tetrasubstituted alkenes

A convenient, general and stereoselective synthesis of trisubstituted alkenes and tetrasubstituted alkenes containing a cyanide function as well as trisubstituted episulphides have been elaborated. Methodology described for the preparation of these compounds is based on the corresponding readily available selenophosphates 1 and thiophosphates 2.     

A general method for the solid-phase synthesis of unsymmetrical tri- and tetrasubstituted ureas

A general method for the preparation of unsymmetrical di, tri-, and tetrasubstituted ureas on polymer supports is presented. Polymer-bound primary and secondary amines react with imidazolium salts (urea donors), which are generated from the reaction of N,N'-carbonyldiimidazole (CDI) with primary and secondary amines followed by alkylation with MeI to give tri- and tetrasubstituted ureas in excellent yields (76-98%) and purities (80-99%).     

Regio- and stereoselective synthesis of Z-vinylic tellurides from propargylic alcohols: a route to chiral Z-enynes

tert-Butyldimethylsilyl ethers of propargylic alcohols are hydrotellurated regioselectively to give 1,2-Z-vinylic tellurides. Enantiomerically pure propargylic alcohols give enantiomerically pure vinylic tellurides, which are coupled with alkynes under Pd catalysis to give enantiomerically pure allylic enynols.     

Flexible synthesis of enantiomerically pure 2,8-dialkyl-1,7-dioxaspiro[5.5]undecanes and 2,7-dialkyl-1,6-dioxaspiro[4.5]decanes from propargylic and homopropargylic alcohols

A new approach to enantiomerically pure 2,8-dialkyl-1,7-dioxaspiro[5.5]undecanes and 2,7-dialkyl-1,6-dioxaspiro[4.5]decanes is described and utilizes enantiomerically pure homopropargylic alcohols obtained from lithium acetylide opening of enantiomerically pure epoxides, which are, in turn, acquired by hydrolytic kinetic resolution of the corresponding racemic epoxides. Alkyne carboxylation and conversion to the Weinreb amide may be followed by triple-bond manipulation prior to reaction with a second alkynyllithium derived from a homo- or propargylic alcohol. In this way, the two ring components of the spiroacetal are individually constructed, with deprotection and cyclization affording the spiroacetal. The procedure is illustrated by acquisition of (2S,5R,7S) and (2R,5R,7S)-2-n-butyl-7-methyl-1,6-dioxaspiro[4.5]-decanes (1), (2S,6R,8S)-2-methyl-8-n-pentyl-1,7-dioxaspiro[5.5]undecane (2), and (2S,6R,8S)-2-methyl-8-n-propyl-1,7-dioxaspiro[5.5]undecane (3). The widely distributed insect component, (2S,6R,8S)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane (4), was acquired by linking two identical alkyne precursors via ethyl formate. In addition, [(2)H(4)]-regioisomers, 10,10,11,11-[(2)H(4)] and 4,4,5,5-[(2)H(4)] of 3 and 4,4,5,5-[(2)H(4)]-4, were acquired by triple-bond deuteration, using deuterium gas and Wilkinson's catalyst. This alkyne-based approach is, in principle, applicable to more complex spiroacetal systems not only by use of more elaborate alkynes but also by triple-bond functionalization during the general sequence.     

Water as an additive for selective synthesis of saturated 1,4-diketones and tetrasubstituted furans directly from 1,4-enediones

Water-controlled and phosphine-mediated selective synthesis of saturated 1,4-diketones and tetrasubstituted furans has been developed directly from 1,4-enediones. Saturated 1,4-diketones were selectively obtained in acetone with water as an additive, whereas tetrasubstituted furans were selectively obtained in anhydrous 1,2-dichloroethane. A large variety of functional groups are tolerated under these reaction conditions, including electron-rich, electron-poor, halogen, and heteroaryl substituents. This method also has significant advantages in easily available substrates, mild reaction conditions, and high reaction efficiency.     

A new and general one-pot synthesis of propargyl alcohols from esters

Intermediates easily prepared by partial reduction of various esters with LDBBA as a reducing agent smoothly react with lithium acetylides to give propargyl alcohols, without isolation of partial reduction intermediates, in good yields (73-83%).     

A novel route to thioketenes by flash vacuum thermolysis of silylatedketene dithioacetals,synthesis of propadienethione.

Flash vacuum thermolysis (fvt) of silylated ketene dithioacetals 2 leads to reactive thioketenes 1. This method, added to a retrodienic reaction, allowedaccess to propadienethione 3.     

Stereoselective synthesis of novel five-membered homoazasugars. A convenient route to all-cis tetrasubstituted pyrrolidines

We present a highly stereoselective procedure for the preparation of (2S and 2R,3S,4R,5S)-5-methyl-3,4-dihydroxy-2- ethoxycarbonylmethylpyrrolidines based on conjugate addition of ammonia to unsaturated aldonic esters derived from d-ribose followed by tandem cyclization. Derivatisation of these compounds to 2-hydroxyethyl-, benzymidazolylmethyl-, biphenyl-1-aminoethyl and naphthalene-l-aminoethyl-pyrrolidines is also presented.     

A novel general route for the synthesis of C-glycosyl tyrosine analogues

A general method for the synthesis of C-glycosyl amino acids is described here. The stereoisomerically pure tyrosine analogues alpha-L-4 and beta-L-6 are prepared in reasonable overall yields from allyl derivatives 10 and 11. The key step is a benzannulation procedure which is employed in the creation of the aromatic ring that bears the amino acid function.     

A convenient route for the synthesis of s,s-and R,R-warfarin alcohols

S,S-and R,R-warfarin alcohols 3 are prepared in good yield and in 99% d.e. (diastereomeric excess) by the reaction of S- or R-warfarin 1 with S or R-Alpine-Hidride 2.     

Indium-mediated allenylation of arylacyl bromides in a route for the synthesis of substituted furans

A three-step, single purification procedure has been developed for the concise synthesis of substituted furans from arylacyl bromides.     

A general route for the synthesis of β,β-difluorocarboxylic acids

A new method for the preparation of β,β-difluoro- (and other gem-difluoro) acids has been developed. It is based on the fact that 3-oxocarboxylic esters are easy to make and convert to the corresponding dithiane derivatives. These dithianes reacted with BrF₃, a commercial, but rarely used reagent in organic chemistry, under very mild conditions to form the corresponding difluoroesters, which in turn could be quantitatively hydrolyzed to the free gem-difluoroacids.     

A new route to cumulenes by stannylation-deoxystannylation of propargylic alcohols. Application to synthesis of conjugated enyne[3]cumulene as a model compound of neocarzinostatin chromophore

Sequential treatment of a propargylic alcohol by BuLi and Bu₃SnCl gave a mixture of stannylated propargylic alcohol and stannylated allenyl alcohol, both of which were converted to a single [3]cumulene by deoxystannylation of the stannyl alcohols by treatment with methanesulfonyl chloride and triethylamine. The efficiency of the deoxystannylation has been compared with that of an analogous silyl counterpart and proved to be much more efficient. The method has been applied to synthesis of conjugated enyne[3]cumulene 3 as a model compound of neocarzinostatin chromophore.     

An atom-economic and selective ruthenium-catalyzed redox isomerization of propargylic alcohols. An efficient strategy for the synthesis of leukotrienes

Catalytic ruthenium complexes in conjunction with an indium cocatalyst and Bronsted acid isomerize primary and secondary propargylic alcohols in good yields to provide trans enals and enones exclusively. Readily available indenylbis(triphenylphosphine)ruthenium chloride, in the presence of indium triflate and camphorsulfonic acid, gives the best turnover numbers and reactivity with the broadest range of substrates. Deuterium labeling experiments suggest that the process occurs through propargylic hydride migration followed by protic cleavage of the resultant vinylruthenium intermediate. Application of this method to the synthesis of leukotriene B4 demonstrates its utility and extraordinary selectivity.     

Strategy for cyclopentenone annulation of olefins: A general protocol for bicyclo [n.3.0] enone synthesis

Several bicyclic α-chloro enones obtained through Greene annulation of cyclic olefins are shown to undergo efficient, two step, enone transposition $\text{via}$ Luche reduction and aq. formic acid treatment. Application of this methodology to the formal synthesis of exaltone^® and (±)-muscone is described.