Meerwein–Ponndorf–Verley alkynylation of aldehydes

Org. Biomol. Chem., 2004, 2, 3312 - 3319,

In 1925 Meerwein1 and Verley2 independently reported the reduction of aldehydes with primary alcohols in the presence of aluminium ethoxide, and in the next year Ponndorf3
extended the scope to the reduction of ketones using second-ary alcohols and their aluminium alkoxides, particularly aluminium isopropoxide (Al(OPri)3). This type of reaction, i.e., Meerwein–Ponndorf–Verley (MPV) reduction is believed to proceed via a six-membered transition state [A] and can be performed under mild conditions both in the laboratory and on a large scale without sophisticated experimental technique, generally exhibiting high chemoselectivity (Scheme 1).4
Accordingly, numerous studies have been carried out to expand the inherent potential of this classical yet important organic transformation as exemplified by the recent elaborations of
lanthanides and transition metal catalysts as well as modified aluminium alkoxides.5,6 During our continuous effort toward the development of new MPV reduction systems, we have been
interested for some time in the possibility of alkyl transfer through the MPV process, which should provide a practical, nonorganometallic way for carbonyl alkylation.7–9 However, developing the MPV alkylation seemed to be a great challenge because of the inertness of alkyl transfer [B] compared to the facile hydride transfer [A] in the MPV reduction.

The MPV reduction was largely supplanted in the late 1950s by methods utilizing boro and aluminum hydrides