Asymmetric Diels-Alder reactions of chiral N-methacryloylsultams with 1,3-dienes

✍ Scribed by Wolfgang Oppolzer; Boris M. Seletsky; Gérald Bernardinelli

• Publisher: Elsevier Science
• Year: 1994
• Tongue: French
• Weight: 365 KB
• Volume: 35
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)73222-9

✦ Synopsis

R2AlC~-ordinate ~-meth~~loy~ul~ lc undergoes efficient, t&o-selective and highly diastereofact controlled [4+2]-additions to cyclopentadiene, isoprene, fE)-piperylene and the 2-silyloxydieaes 10 and 12. The resulting crystalline cyclogdducts are smoothly reduced with LiAlH4 providing the recovered auxiliary and the corresponding enantiomericaIly pure alcohols. Face-selective [4+2]-cycloadditions of C(a)-substituted enoyl dienophiles offer the attractive possibitity of constructing a quaternary center of chirality together with up to three more centers in a single step. ls2) Encouraged by the efficient and practical use of bornanesultam 3a) and toluenesultam 3b) auxiliaries in asymmetric Diels-Alder reactions of C(u)-non-substituted dienophiles A, we thus explored the additions of C(a)-substituted iV-enoylsultums to 1,3-dienes. N-Methacryloylsultams la 4, (m.p. 175-177'(Z), lb 4, (oil) and lc 4, (m.p. 75'C) were readily obtained in 79-95% yield by acylation of the corresponding sultams 7) with methacryloyl chloride in the presence of NaH or Et,N.3) Dienophiles la, lb and lc underwent smooth, Et2AlCI promoted [4+2]-cycloadditions to a range of 1,3dienes at -90 to -20'C. Our results are summarized in Schemes 2,3 and Table 1. 8, First, we studied the additions of iV-methacryloylsultams la, lb and lc to cyclopentadiene (Scheme 2).