CH CH +
CH C-CH2Br + :PPh3 -------> CH C-CH2-PPh3 + 2Br- (phosphonium
CH C-CH2Br + :PPh3 CH C-CH2-PPh3 salt)
CH CH +
Deprotonation with n-butyl lithium (or probably a milder base) to give double ylid
CH + CH - +
CH C-CH2-PPh3 + 2LiC4H9- ------> CH C-CH-PPh3 + 2LiBr + 2C4H10
CH C-CH2-PPh3 CH C-CH-PPh3
CH + CH - +
Addition to 2,3-butanedione
CH - + CH3 CH CH
CH C-CH-PPh3 + O=C ------> CH C C-CH3
CH C-CH-PPh3 O=C CH C C-CH3
CH - + CH3 CH CH
4 step, 4 carbon addition
------> CH CH CH
--------> CH C C C-CH3
--------> CH C C C-CH3 repeat... ----------> CH CH CH
This structure might be useful unfunctionalized, but, since it's symmetrical, would be hard to attach groups on one side only. Of course, you could put groups on both sides simultaneously, but would be wasteful if they were motor binding sites.
Convergently would go faster:
CH CH CH CH
CH C C-CH3 + NBS, 2PPh3, 2RLi, O=C C C-CH3
CH C C-CH3 O=C C C-CH3
CH CH CH CH
------>
-------->
-------->
---------->
CH CH CH CH CH
CH C C C C C-CH3
CH C C C C C-CH3
CH CH CH CH CH
4 step, 12 carbon addition.
I'm currently trying to find the stiffest, easiest to synthesize, easiest to functionalize on one side (or leave it bare) potential strut.
John Michelsen