A Route to Carbasugar Analogues - Jonathan Clayden - The ...

1.4 – Metal complexation
LiAlH 4
R
i) NuLi
or MeLi
+
Mn(CO) 3 Mn(CO) ii) O 2
3
87 88 R = H, Me
Entry R Nu 89 / %
a Me LiCHPh 2 73
b Me LiC(CN)Me 2 58
c Me LiCMe 2 CO 2 Et 43
d H LiCHPh 2 77
e H LiC(CN)Me 2 88
f H LiCMe 2 CO 2 Et 91
R
Nu
±89
51
Table 1.14 – dearomatising additions to Mn(CO) 3 complexes
Complex 88 is only moderately electrophilic in character, and attempted isolation
gives mostly rearomatised adduct, with trace amounts of regioisomeric dienes. Unless
reacting with strong nucleophiles as above, activation of 88 is required, and has been
achieved by ligand exchange, forming a cationic η 5 -complex 90 which is more reactive
than the original η 6 -complex. 56 Addition to this complex may now be performed by
soft carbon nucleophiles or borohydride.
i) RM
R
iii) NuM
R
Mn(CO) 3
+
ii) NOPF 6
Mn(CO) 2 NO
iv) Me 3 NO
Nu
87
90
±89
Entry RM Nu 89 / %
a MeLi NaCH(CO 2 Et)(COMe) 67
b MeLi NaCH(CO 2 Et)CN 59
c MeLi NaCH(CO 2 Me)(SO 2 Ph) 67
d PhMgBr NaCH(CO 2 Et)(COMe) 66
e PhMgBr NaCH(CO 2 Et)CN 59
f PhMgBr NaCH(CO 2 Me)(SO 2 Ph) 62
g PhMgBr NaBH 4 85
51
Table 1.15 – activation of Mn(CO) 3 complexes
46