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Thomas Wynn

Publications and source records attributed to Thomas Wynn.

4 recordsLinked to original sources
PubMed2002

Lewis base activation of lewis acids. Addition of silyl ketene acetals to aldehydes.

The weak Lewis acid silicon tetrachloride can be activated by catalytic amounts of the chiral bisphosphoramide (R,R)-3 to form a highly reactive, chiral trichlorosilyl cation which is an extremely effective promoter of aldol addition reactions between aldehydes and silyl ketene acetals. The tert-butyldimethylsilyl ketene acetal of methyl acetate adds nearly instantaneously to aromatic and olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl ether adducts.

Journal Article↗
PubMed2002

Archaeology and cognitive evolution.

Archaeology can provide two bodies of information relevant to the understanding of the evolution of human cognition--the timing of developments, and the evolutionary context of these developments. The challenge is methodological. Archaeology must document attributes that have direct implications for underlying cognitive mechanisms. One example of such a cognitive archaeology is found in spatial cognition. The archaeological record documents an evolutionary sequence that begins with ape-equivalent spatial abilities 2.5 million years ago and ends with the appearance of modern abilities in the still remote past of 400,000 years ago. The timing of these developments reveals two major episodes in the evolution in spatial ability, one, 1.5 million years ago and the other, one million years later. The two episodes of development in spatial cognition had very different evolutionary contexts. The first was associated with the shift to an open country adaptive niche that occurred early in the time range of Homo erectus. The second was associated with no clear adaptive shift, though it does appear to have coincided with the invasion of more hostile environments and the appearance of systematic hunting of large mammals. Neither, however, occurred in a context of modern hunting and gathering.

Animals↗