Enantioselective and Diastereoselective Additions of Allylic Stannanes to Aldehydes Promoted by a Chiral (Acyloxy)borane Catalyst
作者:James A. Marshall、Michael R. Palovich
DOI:10.1021/jo980145c
日期:1998.6.1
A modified Yamamoto Lewis acid (CAB), prepared from the 2,6-dimethoxybenzoic ester of (R-R)-tartaric acid, and 1.5 equiv of BH3.THF was employed in additions of crotyltributyltin (6) and allyltributyltin (9) to representative achiral aldehydes in the presence of 2 equiv of (CF3CO)(2)O. The crotyltin additions proceeded with good to excellent diastereoselectivity and enantioselectivity affording the syn adducts 7a-e of 70-90% ee as major products (78:22-92:8). Addition of allylstannane 9 to cyclohexanecarboxaldehyde (1a) afforded the (R)-adduct of only 55% ee. In contrast, the use of Keck's BINOL catalyst gave 10, the allyl adduct of la, of 87% ee. However, addition of the crotylstannane to 1a with this catalyst led to a 65:35 mixture of syn and anti adducts 7a and 8a of 95% and 49% ee. Additions of crotylstannane 6 to (R)- and (S)-2-methyl-3-ODPS-propanal [(R)-11 and (S)-11] promoted by the modified CAB Lewis acid afforded the syn,syn and syn,anti products 12 and 14 in large predominance (98:2 and 90:10), indicative of effective complex control in the transition state. The results are consistent with the Corey H-bonded aldehyde transition-state proposal.
MULZER, J.;AUTENRIETH-ANSORGE, L.;KIRSTEIN, H.;MATSUOKA, TOSHIKAZU;MUNCH,+, J. ORG. CHEM., 52,(1987) N 17, 3784-3789
Addition of Dithiols to Bis-Ynones: Development of a Versatile Platform for the Synthesis of Polyketide Natural Products
作者:Helen F. Sneddon、Matthew J. Gaunt、Steven V. Ley
DOI:10.1021/ol034248f
日期:2003.4.1
[reaction: see text] The conjugate addition of dithiols to bis-ynones generates a versatile masked 1,3,5-triketone platform. These functional units are useful intermediates for the synthesis of oxygen-containing heterocycles commonly found in polyketide natural products. The tetrahydropyranyl fragments of the marine macrolides Lyngbouilloside and Callipeltoside A have been synthesized with use of this