Ynoate substrates

An expedient method for the preparation of isochromene carboxylates (203) has been developed, which relies on the regioselective 1,6-addition of various nucleophiles, such as Grignard reagents, alkoxides, and cyanide, to benzopyranylidenetungsten(O) complexes (201), followed by iodine oxidation of the addition intermediates (202)254 DFT calculations have been carried out to rationalize the unusual switch in stereoselectivity, where ynone and ynoate substrates exhibit opposite stereochemical preferences in the stannylcupration.255... 

Dienes. Addition of alkenes to alkynes (ene-type reaction) is readily promoted by the Ru complex. Branched products are favored, and functional groups in the substrates are tolerated. Internal alkynes also undergo this addition. The 2 1 adduct from 1,11-dodecadiene and ethyl 4-hydroxypent-2-ynoate is a precursor of ancepsenolide. ... 

It is important to note that both aliphatic and aromatic vinyl ketones were viable substrates in which P-alkyl and P-aryl substitutions were tolerated. Diaryl alkynes, mono-aryl internal alkynes, nonaromatic internal alkynes, terminal alkynes, and free hydroxyl-bearing alkynes were all efficient participants. It should be mentioned that while ynoates were successful nucleophiles, enoate electrophiles were found to be poor participants in nickelotalyzed couplings. 

Michael addition to substituted enoates has proven diastereo-selective. Ethyl ( )-crotonate or ethyl ( )-cinnamate afforded conjugate addition adducts in 92% yield and 87% yield with anfi/sj73-diastereomeric ratios of 85/15 and 100/0, respectively (eq 10) whereas in the presence of HMPA the diastereoselectiv-ity was reversed. With the y-oxygenatedenoate, anfr-diastereo-selectivity resulted HMPA improved the selectivity from 8/1 to 12/1 (eq 11). Similar results were obtained with a conjugated lactone (eq 12). Ethyl ynoate also acted as a reactive Michael receptor for the methallyl sulfone (eq 13). Other conjugated substrates such as nitroolefins and acrylonitrile proved to be appropriate Michael receptors as well. 

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