Menthyl propiolate

Diastereoselective Diels-Alder reactions The (S)- and (R)-3-(2-pyridylsul-finyl)acrylates (1) are obtained by addition of 2-mercaptopyridine to ( + )-menthyl propiolate followed by oxidation and fractional crystallization of the diastereoiso-meric sulfoxides. In the presence of (QH AIG, both undergo highly diastereoselective Diels-Alder reactions with furan to give mainly endo-adducts without epimerization of the sulfoxide group. The products are converted as shown into ( + )- and ( - )-ewdo-2-hydroxymethyl-7-oxabicyclo[2.2.1]heptane (2). 

Lithium borohydride-N, N -Dibenzoyl-cystine, 92 Menthol, 172 Menthyl propiolate, 173 Menthyl 3-(2-pyridyl)sulfinylacrylate, 173... 

The rather low reactivity of the 3-p-tolylsulfinyl acrylates (they do not react with furan even under forcing conditions) prompted the search for more reactive dienophiles. In this context, pyridylsulfinyl derivatives proved to be more efficient than the arylsulfinyl ones. Thus, menthyl-3-(2-pyridylsulfinyl)propenoates 14a and 14b were prepared from (+)-menthyl propiolate in low yields [34]. Their reactions with cyclopentadiene proceed smoothly in the presence of Et2AlCl at -70°C to afford just one endo diastereoisomer 15a or 15b [35] (in the absence of the catalyst the 7r-facial selectivity for the endo approach was lower than that observed for the p-tolylsulfmyl derivatives [10c]). These compounds were transformed into 16a or 16b [36] respectively (Scheme 8), both allowing the synthesis of the bicyclic lactone 17 (known as Ohno s lactone), a key intermediate in Ohno s synthesis of (-)-aristeromycin and (-)-neplanocin A [37]. 

Nakako, H. Nomura, R. Tabata, M. Masuda, T. Synthesis and structure in solution of poly[(-)-menthyl propiolate as a new class of helical polyacetylene. Macromolecules 1999, 32, 2861-2864. 

Recently, Li and co-workers re X)rted superior enantioselectivity in vinylcupration of a series of aldehydes starting with menthyl propiolates (53). While MBH reaction of menthyl acrylates provides < 20% ee, vinylcupration provides 50-87% ee. The enantioselectivities obtained in the MBH reaction of benzaldehyde with menthyl, isopinocampheyl and isocaranyl acrylates were in the same range (< 20%). Comparison of Greene s results (75) on asymmetric vinylalumination, and Li s asymmetric vinylcupration of benzaldehyde (55) starting with menthyl propiolate shows that vinylcupration provides better enantioselectivity. These results point to the fact that asymmetric vinylcupration of fluoro-carbonyl compounds with these auxiliaries should be a worthwhile project. 

---