Reaction with methyl propargyl ether

The use of Rh2(5/ -MEPY)4 and Rh2(55-MEPY)4 for reactions with menthyl diazoacetates (MDA) also produces an enormous double diastereoselection not previously observed to the same degree in cyclopropanation reactions. With methyl propargyl ether, for example, Rh2(5/ -MEPY)4 catalyzed reactions of d-MDA yield 16 (R = CH3OCH2) in 98% diastereomeric excess (de), but /-MDA produces its diastereoisomer in only 40% de with Rh2(55-MEPY)4, /-MDA gives the higher de (98%) and d-MDA gives the lower de (43%). Similar results are obtained from reactions of MDA with 1-hexyne and 3,3-dimethyl-1-propyne. The diazocarboxylate substituent obviously plays a critical role in establishing the more effective carbene orientation for addition to the alkyne. 

Other examples of preparative routes relying on reactions with electrophiles have been used in the syntheses of thieno[2,3-y][l,2,3,4,5]pentathiepin by treatment of tetrahydrothiophene with S2CI2 in the presence of DABCO <05OBC3496> and indium nonaflate [In(ONf)3] catalyzed annulation of the 2,2 -bithiophene 62 with methyl propargyl ether leading to the system 63 <05AG(E)1336>. 

The flask was charged with 2.0 mol of dry, freshly distilled (note 1) methyl propargyl ether (VIII-6, Exp. 7), potassium iert.-butoxide (note 2) (5 g) was added with stirring and the mixture was heated under reflux. The reaction was... 

Reaction of 13-Dipotassiated Methyl Propargyl Ether with Bromohexane... 

Under the catalytic action of Rh2(OAc)4, formation of a propargylic ether from a terminal alkyne (229, R1=H) is preferred as long as no steric hindrance by the adjacent group is felt162,218>. Otherwise, cyclopropenation may become the dominant reaction path [e.g. 229 (R1 = H, R2 = R3 = Me) and methyl diazoacetate 56% of cyclopropene, 36% of propargylic ether162)], in contrast to the situation with allylic alcohols, where O/H insertion is rather insensitive to steric influences. 

ROC==CCH -> ROCHjC CH. Propynyl ethers can be obtained from secondary alkoxides by reaction with trichloroethylene followed by dehydrochlorination and methylation. These can be rearranged to propargyl ethers by KAPA. This sequence is applicable to highly hindered secondary alcohols.1... 

Another ingenious variation starts with 4-methoxypropargylamines 36 which are readily accessible via copper-catalyzed Mannich reaction of propargyl ethers U9>. The group R can again only be a hydrogen atom or methyl group. 

Enantioselective Intermolecular Cyclopropenation Reactions. The use of Rh2(MEPY)4 catalysts for intermolecular cyclopropenation of 1-alkynes results in moderate to high selectivity. With propargyl methyl ether (or acetate), for example, reactions with (—)-menthyl [(+)-(l/ ,25,5/ )-2-isopropyT5-methyl-1-cyclohexyl] diazoacetate catalyzed by Rh2(55 -MEPY)4 produces the corresponding cyclopropene product (eq 3) with 98% diastere-omeric excess (de). ... 

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